Albinism<\/h1>\r\n<\/div>\r\nThis child has much lighter skin and\u00a0hair\u00a0than his parents. He has a condition called albinism<\/a>, which results from a\u00a0lack of\u00a0the\u00a0pigment melanin in the\u00a0skin,\u00a0hair, and\u00a0eyes. Although\u00a0he\u00a0looks<\/em>\u00a0different than his parents, albinism is actually a genetic trait.\u00a0Genetic traits<\/strong>\u00a0are characteristics that are encoded in\u00a0DNA. Most forms of albinism are recessive, which\u00a0is why\u00a0the child's\u00a0parents were able to\u00a0pass\u00a0the trait to him without exhibiting the condition themselves. You will learn more about this type of inheritance\u00a0in this concept.\u00a0Albinism is\u00a0one of the few human traits that actually has a simple inheritance pattern,\u00a0similar to\u00a0the traits that Gregor\u00a0Mendel<\/a>\u00a0studied in\u00a0pea plants. The way these traits are inherited by offspring from their parents is called [pb_glossary id=\"2515\"]Mendelian inheritance[\/pb_glossary].\r\n\r\nWhat Is Mendelian Inheritance?<\/h1>\r\n<\/div>\r\nMendelian inheritance<\/strong>\u00a0refers to the inheritance of traits controlled by a single gene with two\u00a0[pb_glossary id=\"5449\"]alleles[\/pb_glossary], one of which may be completely [pb_glossary id=\"5971\"]dominant[\/pb_glossary] to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on [pb_glossary id=\"2112\"]autosome[\/pb_glossary]s, or by genes on [pb_glossary id=\"2125\"]sex\u00a0chromosomes[\/pb_glossary].\r\n\r\n \t- Autosomal traits<\/strong>\u00a0are controlled by genes on one of the 22 pairs of human [pb_glossary id=\"2112\"]autosomes[\/pb_glossary]. Autosomes are all the\u00a0chromosomes\u00a0except the X or Y chromosome, and they do not differ between males and females, so autosomal traits are inherited in the same way, regardless of the sex of the parent or offspring.<\/li>\r\n \t
- Traits controlled by genes on the sex\u00a0chromosomes\u00a0are called\u00a0[pb_glossary id=\"2516\"]sex-linked traits[\/pb_glossary].<\/strong>\u00a0Because of the small size of the Y chromosome, most sex-linked traits are controlled by genes on the X chromosome. These traits are called\u00a0[pb_glossary id=\"2517\"]X-linked traits[\/pb_glossary]<\/strong>. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits, because males have just one X chromosome. In addition, males always inherit their X chromosome from their mother, and they pass on their X chromosome to all of their daughters, but none of their sons.<\/li>\r\n<\/ul>\r\n\r\n
Studying Inheritance Patterns<\/h1>\r\n<\/div>\r\nThere are two very useful tools for studying how traits are passed from one generation to the next. One tool is a\u00a0pedigree, and the other is a Punnett square.\r\nPedigree<\/h2>\r\nThe chart below (Figure 5.13.2) is called a [pb_glossary id=\"2519\"]pedigree[\/pb_glossary]<\/strong>. A pedigree shows how a trait is passed from generation to generation within a family.\u00a0A pedigree can show, for example, whether a Mendelian trait is an [pb_glossary id=\"2112\"]autosomal[\/pb_glossary] or [pb_glossary id=\"2517\"]X-linked[\/pb_glossary] trait. It can also be used to infer the genotype of different members of the family.\r\n\r\nThe trait represented by\u00a0this\u00a0chart is a hypothetical autosomal trait controlled by a dominant allele. At the top of the pedigree, you can see symbols representing a married couple. The husband\u00a0has<\/em> the trait (affected male), but the wife does not (unaffected female). The next row of the pedigree shows the couple's children, as well as the spouses of three of the children. For example, the first child on the left is an affected male married to an unaffected female. The third row of the pedigree shows the next generation (the grandchildren of the couple at the top of the pedigree). One child in this generation \u2014 the affected female on the left \u2014 is the sibling of an unaffected male.\r\n\r\n[caption id=\"attachment_2518\" align=\"aligncenter\" width=\"666\"]![\"Shows](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Pedigree_Chart2.svg_-2.png\")
Figure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em>[\/caption]\r\n\r\n\r\n\r\nPunnett Square<\/span>\r\n\r\n<\/div>\r\nA\u00a0[pb_glossary id=\"2520\"]Punnett square[\/pb_glossary]<\/strong> is a chart that allows you to easily determine the expected ratios of possible genotypes in the offspring of two parents. You can see a hypothetical example in Figure 5.13.3. In this case, the gene is autosomal, and both parents are heterozygotes (Aa)<\/em>\u00a0for the gene. Half of the gametes produced by each parent will have the\u00a0A<\/em>\u00a0allele, and half will have the\u00a0a<\/em> allele. That's because the two\u00a0alleles\u00a0are on homologous chromosomes, which always separate and go to separate gametes during\u00a0meiosis. The alleles in the gametes from each parent are written down the side and across the top of the Punnett square. Filling in the\u00a0cells\u00a0of the Punnett square gives the possible genotypes of their children. It also shows the most likely ratios of the genotypes, which in this case is 25 per cent\u00a0AA,<\/em> 50 per cent\u00a0Aa,<\/em> and 25 per cent\u00a0aa.<\/em>\r\n\r\n[caption id=\"attachment_2521\" align=\"aligncenter\" width=\"816\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Punnett-square-2.png\")
Figure 5.13.3 A Punnett square shows the most likely proportions of offspring by genotype for a particular mating type.<\/em>[\/caption]\r\n\r\n\r\n\r\nA Punnett square can also be used to show how the X and Y chromosomes are passed from parents to their children. This is illustrated in the Punnett square in Figure 5.13.4<\/span>. It may help you understand the inheritance pattern of sex-linked traits.<\/span>\r\n\r\n[caption id=\"attachment_2522\" align=\"aligncenter\" width=\"295\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/f-d_0018fb7c7f3506876764d9d02d846116f8ed3a0040ed8a65cfc6be14IMAGE_THUMB_POSTCARD_TINYIMAGE_THUMB_POSTCARD_TINY-2.png\")
Figure 5.13.4 Inheritance of Sex Chromosomes. Mothers pass only X chromosomes to their children. Fathers always pass their X chromosome to their daughters, and their Y chromosome to their sons. Can you explain why fathers always determine the sex of the offspring?<\/em>[\/caption]\r\n\r\n<\/div>\r\n\r\n\r\nHere's how to fill out a Punnett Square:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=prkHKjfUmMs&t=\r\nLearn Biology: How to Draw a Punnett Square, mahalodotcom, 2011.<\/p>\r\nTry out this Punnett Square:\r\n\r\n[h5p id=\"507\"]\r\n
Autosomal Mendelian Traits in Humans<\/h1>\r\n<\/div>\r\nNot many human autosomal traits are controlled by a single gene with two\u00a0alleles, but they are a good starting point for understanding human heredity. As discussed in the beginning of this concept, most forms of albinism in humans have\u00a0a Mendelian inheritance pattern.\u00a0Albinism\u00a0is usually controlled by a single autosomal gene with two alleles. The\u00a0allele\u00a0for normal pigmentation (let's call it\u00a0R<\/em>) is dominant to the\u00a0allele\u00a0for albinism (r<\/em>). Individuals with either an\u00a0RR<\/em>\u00a0or\u00a0Rr\u00a0<\/em>genotype will not have albinism, because the\u00a0R<\/em>\u00a0allele\u00a0is dominant over the recessive\u00a0r<\/em>\u00a0allele.\r\n\r\nHowever,\u00a0consider what happens if two individuals with the\u00a0Rr<\/em>\u00a0genotype reproduce with each other. The outcome\u00a0would be\u00a0similar to\u00a0the example shown in the Punnett square\u00a0above\u00a0for two hypothetical\u00a0Aa<\/em>\u00a0individuals.\u00a0Their possible\u00a0offspring\u00a0could be\u00a0RR<\/em>\u00a0(normal pigmentation),\u00a0Rr<\/em>\u00a0(normal pigmentation), or\u00a0rr<\/em>\u00a0(albinism). This explains why a child with albinism (rr<\/em>), can have two parents that do not have albinism. Both unaffected parents must be a carrier of the recessive\u00a0r<\/em>\u00a0allele, but they also have a dominant\u00a0R <\/em>allele that prevents them from having the condition themselves.\r\n\r\nSome other human traits that\u00a0have a\u00a0Mendelian inheritance pattern\u00a0are Huntington's disease and\u00a0wet\u00a0versus\u00a0dry ear wax. You may have heard about other human traits that were\u00a0previously<\/em>\u00a0thought to be Mendelian,\u00a0such as dimples, a widow's peak hairline, hitchiker's thumb, and the ability to roll your tongue. As science has progressed, it is now understood that these are not actually Mendelian traits. In fact, most human traits are actually controlled by multiple genes, or otherwise have more than two alleles,\u00a0which means they\u00a0do not have\u00a0a\u00a0simple Mendelian inheritance pattern.\r\n\r\nX-Linked Mendelian Traits in Humans<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_2525\" align=\"alignright\" width=\"366\"]![\"Shows](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Red-Green-Colour-Blindness-2.png\")
Figure 5.13.5 This circle of colours containing the number 74 is part of the Ishihara colour blindness test.<\/a><\/em>[\/caption]\r\n\r\nBecause males have just one X chromosome, they have only one allele for any X-linked trait. Therefore, a recessive X-linked allele is always expressed in males. Because females have two X chromosomes, they have two alleles for any X-linked trait. Therefore, they must inherit two copies of the recessive allele to express an X-linked recessive trait. This explains why X-linked recessive traits are less common in females than males, and why they show a different pattern of inheritance than autosomal traits.\r\n\r\n[caption id=\"attachment_2527\" align=\"alignleft\" width=\"334\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/XlinkRecessive-1-2.jpg\")
Figure 5.13.6 Heredity implications of an X-linked recessive gene carried by the mother. <\/em>[\/caption]\r\n\r\nAn example of a recessive X-linked trait is red-green colour blindness. People with this trait cannot distinguish between the colours red and green. More than one recessive gene on the X chromosome codes for this trait, which is fairly common in males, but relatively rare in females. Figure 5.13.6 shows a simple pedigree for this trait. A female with one of the recessive alleles for the trait does not have the trait herself, but can pass it on to her children. In this case, she is called a carrier of the trait. Half of any sons she has can be expected to have the trait, because there is a 50 per cent chance that they will inherit the X chromosome with the colour-blindness allele. Having only one X chromosome, the recessive allele will be expressed in the sons who inherit it. However, as long as the father is not affected, none of the woman's daughters will have the trait. The daughters have a 50 per cent chance of inheriting the X chromosome with the colour-blindness allele, but it won't be expressed because it is recessive to the normal allele they inherit from their father.\r\n\r\n[caption id=\"attachment_2529\" align=\"alignright\" width=\"282\"]![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/The_Young_Queen_Victoria-2.jpg\")
Figure 5.13.7 Queen Victoria carried hemophilia and she passed the hemophilia allele to two of her daughters and one of her sons. This portrait of her was painted in the 1840s.<\/em>[\/caption]\r\n\r\nAnother example of a recessive X-linked Mendelian trait is hemophilia, which is a disorder characterized by the blood's inability to clot normally. England's Queen Victoria (pictured in Figure 5.13.7) carried the disorder. Two of her five daughters inherited the hemophilia allele from their mother and were carriers. When they married royalty in other European countries, they spread the allele across Europe, including to the royal families of Spain, Germany, and Russia. Victoria's son Prince Leopold also inherited the hemophilia allele from his mother, and he actually suffered from the disease. Understandably, hemophilia was once popularly called \"the royal disease.\"\r\n\r\n\r\n \r\n\r\nFeature: My\u00a0Human Body<\/span>.\r\n\r\n<\/div>\r\nAre you colour blind, or do you think you might be? If you inherited this X-linked recessive disorder, a world without clear differences between certain colours seems normal to you. It's all you have ever known! Some people who are colour blind are not even aware of it. Simple tests have been devised to determine whether a person is colour blind, and to what degree. An example of such a test is pictured in Figure 5.13.5. What do you see when you look at this circle? Can you clearly perceive the number 74? If so, you probably have normal red-green colour vision. If you cannot see the number, you may have red-green colour blindness.\r\n\r\n[caption id=\"attachment_2530\" align=\"aligncenter\" width=\"484\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Deuteranopia-2.jpg\")
Figure 5.13.8 Perception of colours comparison.<\/em>[\/caption]\r\n\r\nBeing colour blind can cause a number of problems. These may range from minor frustrations to outright dangers. Here are a few examples:\r\n\r\n \t- If you are colour blind, it may be difficult to colour-coordinate clothing and furnishings. You may end up wearing colour combinations that people with normal colour vision think are odd or clashing.<\/li>\r\n \t
- Many LED indicator lights are red or green.\u00a0Power strips and electronic devices, for example, may have indicator lights to show whether they are on (green) or off (red).<\/li>\r\n \t
- Test strips for pH, hard water, swimming pool chemicals, and other common tests are also often colour coded. Litmus paper for testing pH, for example, turns red in the presence of an acid, but if you are colour blind, you may not be able to read the test result.<\/li>\r\n \t
- Do you like your steak well done? If you are colour blind, you may not be able to tell if the meat is still undercooked (red) or grilled just right. You also may not be able to distinguish ripe (red) from unripe (green) fruits and vegetables, such as tomatoes. And some foods, such as dark green spinach, may look more like mud than food, making them totally unappetizing.<\/li>\r\n \t
- Weather maps often are colour coded. Is that rain (green) in your forecast, or a wintry mix of sleet and freezing rain (pink or red)? If you can't tell the difference, you may go out on the roads when you shouldn't, putting yourself in danger.<\/li>\r\n \t
- Being able to distinguish red from green traffic lights may be a matter of life or death. This can be very difficult for someone with red-green colour blindness. In some countries, people with this vision defect are not allowed to drive.<\/li>\r\n<\/ul>\r\n[h5p id=\"508\"]\r\n\r\nFigure 5.13.9\u00a0 Examples of challenges faced by those who are colour blind<\/em>\r\n\r\n
\r\n5.13 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"2515\"]Mendelian inheritance[\/pb_glossary] refers to the inheritance of traits controlled by a single [pb_glossary id=\"5521\"]gene[\/pb_glossary] with two [pb_glossary id=\"5449\"]alleles[\/pb_glossary], one of which may be completely dominant to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on [pb_glossary id=\"2112\"]autosomes[\/pb_glossary], or by genes on [pb_glossary id=\"2125\"]sex chromosomes[\/pb_glossary].<\/li>\r\n \t
- Two tools for studying inheritance are [pb_glossary id=\"2519\"]pedigrees[\/pb_glossary] and\u00a0[pb_glossary id=\"2520\"]Punnett squares[\/pb_glossary]. A pedigree is a chart that shows how a trait is passed from generation to generation within a family. A Punnett square is a chart that shows the expected ratios of possible [pb_glossary id=\"6039\"]genotypes[\/pb_glossary] in the offspring of two parents.<\/li>\r\n \t
- Examples of human autosomal Mendelian traits include albinism and Huntington's disease. Examples of human X-linked traits include red-green colour blindness and hemophilia.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Define genetic traits and Mendelian inheritance.<\/li>\r\n \t
- [h5p id=\"509\"]<\/li>\r\n \t
- Explain why autosomal and X-linked Mendelian traits have different patterns of inheritance.<\/li>\r\n \t
- Identify examples of human autosomal and X-linked Mendelian traits.<\/li>\r\n \t
- Imagine a hypothetical human gene that has two alleles,Q<\/em>and\u00a0q<\/em>.\u00a0Q<\/em>\u00a0is dominant to\u00a0q<\/em>\u00a0and the inheritance of this gene is Mendelian. Answer the following questions about this gene.\r\n
\r\n \t- If a woman has the genotype\u00a0Q q\u00a0<\/em>and her husband has the genotype\u00a0QQ<\/em>, list each of their possible gametes. What proportion of their gametes will have each allele?<\/li>\r\n \t
- What are the likely proportions of their offspring beingQQ<\/em>,Qq<\/em>, or\u00a0qq<\/em>?<\/li>\r\n \t
- Is this an autosomal trait or an X-linked trait? How do you know?<\/li>\r\n \t
- What are the chances of their offspring exhibiting the dominant\u00a0Q\u00a0<\/em>trait? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t
- Explain why fathers always pass their X chromosome down to their daughters.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=emb_logo\r\nPunnett Squares and Sex-Linked Traits, Amoeba Sisters, 2015.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4\r\n
Pedigrees, Amoeba Sisters, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=veB31XmUQm8\r\n
Secrets of the X chromosome - Robin Ball, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.13.1<\/strong>\r\n\r\nAlbino_baby_by_Felipe_Fernandes<\/a>\u00a0by Felipe Fernandes<\/a> on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0) license.\r\n\r\nFigure 5.13.2<\/strong>\r\n\r\nPedigree_Chart2.svg<\/a> by Jerome Walker on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Derivative work of original image<\/a>\u00a0created by\u00a0GAThrawn22<\/a>)\r\n\r\nFigure 5.13.3<\/strong>\r\n\r\nPunnett square by Christine Miller is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.4<\/strong>\r\n\r\nInheritance of Sex Chromosomes<\/a> by CK-12 Foundation<\/a> is used under a CC BY-NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n![\"\"](\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/logo_ck12.png\")
\u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span>![\"CK-12](\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/icon_licence.png\" "\\"CK-12")
<\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 5.13.5<\/strong>\r\n\r\nRed-Green Colour Blindness<\/a> by Unknown author on Wikimedia is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\u00a0(Original believed to be by Shinobu Ishihara<\/a>)\r\n\r\nFigure 5.13.6<\/strong>\r\n\r\nXlinkRecessive<\/a> by US\u00a0National Institutes of Health<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.7<\/strong>\r\n\r\nThe_Young_Queen_Victoria (painted portrait<\/a> by Franz Xaver Winterhalter<\/a> (photograph from the Osborne House, Isle of Wight) on Wikimedia Commoons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.8<\/strong>\r\n\r\nDeuteranopia\/ Figure 9.10<\/a>\u00a0by Web Style Guide<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 5.13.9<\/strong>\r\n\r\n \t- LED traffic light<\/a> by Bidgee<\/a> on Wikimedia <\/i>is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.<\/li>\r\n \t
- Universal indicator paper<\/a> by Bordercolliez<\/a> on Wikimedia <\/em>is used under a CC0 1.0<\/a>\r\nPublic Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en)<\/li>\r\n \t
- Photo tags: Fruit tomatoes food fruits and vegetables fresh<\/a> by InspiredImages<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n \t
- Simple Control with Indicator LIghts<\/a> by Sam D. Wilbur<\/a> on Wikimedia is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/li>\r\n \t
- Photo tags: Feet socks checkered striped pants colorful color<\/a> by Suppenkasper<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\n
References<\/h2>\r\n
Amoeba Sisters. (2015, January 23).\u00a0 Punnett squares and sex-linked traits. YouTube. https:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=youtu.be<\/p>\r\n
Amoeba Sisters. (2017, February 8). Pedigrees. YouTube. https:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4&feature=youtu.be<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 3 Inherited traits of sex chromosomes [digital image]. In CK-12 College Human Biology\u00a0<\/em>(Section 5.12) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/5.12\/<\/p>\r\nmahalodotcom. (2011, January 14). Learn biology: How to draw a punnett square. YouTube. https:\/\/www.youtube.com\/watch?v=prkHKjfUmMs&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 18). Secrets of the X chromosome - Robin Ball. YouTube. https:\/\/www.youtube.com\/watch?v=veB31XmUQm8&feature=youtu.be<\/span><\/p>\r\nWikipedia contributors. (2020, June 26). Albinism in humans. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Albinism_in_humans&oldid=964622728<\/p>\r\nWikipedia contributors. (2020, June 29). Gregor Mendel. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Gregor_Mendel&oldid=965090119<\/p>\r\nWikipedia contributors. (2020, June 17). Ishihara test. In\u00a0Wikipedia. <\/i>https:\/\/en.wikipedia.org\/w\/index.php?title=Ishihara_test&oldid=963014774<\/p>","rendered":"
<\/p>\n![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Albino_baby_by_Felipe_Fernandes_07-2.jpg\")
Figure 5.13.1 Like mother, like son.<\/em><\/figcaption><\/figure>\n\nAlbinism<\/h1>\n<\/div>\n
This child has much lighter skin and\u00a0hair\u00a0than his parents. He has a condition called albinism<\/a>, which results from a\u00a0lack of\u00a0the\u00a0pigment melanin in the\u00a0skin,\u00a0hair, and\u00a0eyes. Although\u00a0he\u00a0looks<\/em>\u00a0different than his parents, albinism is actually a genetic trait.\u00a0Genetic traits<\/strong>\u00a0are characteristics that are encoded in\u00a0DNA. Most forms of albinism are recessive, which\u00a0is why\u00a0the child’s\u00a0parents were able to\u00a0pass\u00a0the trait to him without exhibiting the condition themselves. You will learn more about this type of inheritance\u00a0in this concept.\u00a0Albinism is\u00a0one of the few human traits that actually has a simple inheritance pattern,\u00a0similar to\u00a0the traits that Gregor\u00a0Mendel<\/a>\u00a0studied in\u00a0pea plants. The way these traits are inherited by offspring from their parents is called Mendelian inheritance<\/a>.<\/p>\n\nWhat Is Mendelian Inheritance?<\/h1>\n<\/div>\n
Mendelian inheritance<\/strong>\u00a0refers to the inheritance of traits controlled by a single gene with two\u00a0alleles<\/a>, one of which may be completely dominant<\/a> to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on autosome<\/a>s, or by genes on sex\u00a0chromosomes<\/a>.<\/p>\n\n- Autosomal traits<\/strong>\u00a0are controlled by genes on one of the 22 pairs of human autosomes<\/a>. Autosomes are all the\u00a0chromosomes\u00a0except the X or Y chromosome, and they do not differ between males and females, so autosomal traits are inherited in the same way, regardless of the sex of the parent or offspring.<\/li>\n
- Traits controlled by genes on the sex\u00a0chromosomes\u00a0are called\u00a0sex-linked traits<\/a>.<\/strong>\u00a0Because of the small size of the Y chromosome, most sex-linked traits are controlled by genes on the X chromosome. These traits are called\u00a0X-linked traits<\/a><\/strong>. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits, because males have just one X chromosome. In addition, males always inherit their X chromosome from their mother, and they pass on their X chromosome to all of their daughters, but none of their sons.<\/li>\n<\/ul>\n\n
Studying Inheritance Patterns<\/h1>\n<\/div>\n
There are two very useful tools for studying how traits are passed from one generation to the next. One tool is a\u00a0pedigree, and the other is a Punnett square.<\/p>\n
Pedigree<\/h2>\n
The chart below (Figure 5.13.2) is called a pedigree<\/a><\/strong>. A pedigree shows how a trait is passed from generation to generation within a family.\u00a0A pedigree can show, for example, whether a Mendelian trait is an autosomal<\/a> or X-linked<\/a> trait. It can also be used to infer the genotype of different members of the family.<\/p>\nThe trait represented by\u00a0this\u00a0chart is a hypothetical autosomal trait controlled by a dominant allele. At the top of the pedigree, you can see symbols representing a married couple. The husband\u00a0has<\/em> the trait (affected male), but the wife does not (unaffected female). The next row of the pedigree shows the couple’s children, as well as the spouses of three of the children. For example, the first child on the left is an affected male married to an unaffected female. The third row of the pedigree shows the next generation (the grandchildren of the couple at the top of the pedigree). One child in this generation \u2014 the affected female on the left \u2014 is the sibling of an unaffected male.<\/p>\nFigure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em><\/figcaption><\/figure>\n
What Is Mendelian Inheritance?<\/h1>\r\n<\/div>\r\nMendelian inheritance<\/strong>\u00a0refers to the inheritance of traits controlled by a single gene with two\u00a0[pb_glossary id=\"5449\"]alleles[\/pb_glossary], one of which may be completely [pb_glossary id=\"5971\"]dominant[\/pb_glossary] to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on [pb_glossary id=\"2112\"]autosome[\/pb_glossary]s, or by genes on [pb_glossary id=\"2125\"]sex\u00a0chromosomes[\/pb_glossary].\r\n\r\n \t- Autosomal traits<\/strong>\u00a0are controlled by genes on one of the 22 pairs of human [pb_glossary id=\"2112\"]autosomes[\/pb_glossary]. Autosomes are all the\u00a0chromosomes\u00a0except the X or Y chromosome, and they do not differ between males and females, so autosomal traits are inherited in the same way, regardless of the sex of the parent or offspring.<\/li>\r\n \t
- Traits controlled by genes on the sex\u00a0chromosomes\u00a0are called\u00a0[pb_glossary id=\"2516\"]sex-linked traits[\/pb_glossary].<\/strong>\u00a0Because of the small size of the Y chromosome, most sex-linked traits are controlled by genes on the X chromosome. These traits are called\u00a0[pb_glossary id=\"2517\"]X-linked traits[\/pb_glossary]<\/strong>. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits, because males have just one X chromosome. In addition, males always inherit their X chromosome from their mother, and they pass on their X chromosome to all of their daughters, but none of their sons.<\/li>\r\n<\/ul>\r\n\r\n
Studying Inheritance Patterns<\/h1>\r\n<\/div>\r\nThere are two very useful tools for studying how traits are passed from one generation to the next. One tool is a\u00a0pedigree, and the other is a Punnett square.\r\nPedigree<\/h2>\r\nThe chart below (Figure 5.13.2) is called a [pb_glossary id=\"2519\"]pedigree[\/pb_glossary]<\/strong>. A pedigree shows how a trait is passed from generation to generation within a family.\u00a0A pedigree can show, for example, whether a Mendelian trait is an [pb_glossary id=\"2112\"]autosomal[\/pb_glossary] or [pb_glossary id=\"2517\"]X-linked[\/pb_glossary] trait. It can also be used to infer the genotype of different members of the family.\r\n\r\nThe trait represented by\u00a0this\u00a0chart is a hypothetical autosomal trait controlled by a dominant allele. At the top of the pedigree, you can see symbols representing a married couple. The husband\u00a0has<\/em> the trait (affected male), but the wife does not (unaffected female). The next row of the pedigree shows the couple's children, as well as the spouses of three of the children. For example, the first child on the left is an affected male married to an unaffected female. The third row of the pedigree shows the next generation (the grandchildren of the couple at the top of the pedigree). One child in this generation \u2014 the affected female on the left \u2014 is the sibling of an unaffected male.\r\n\r\n[caption id=\"attachment_2518\" align=\"aligncenter\" width=\"666\"] Figure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em>[\/caption]\r\n\r\n\r\n\r\nPunnett Square<\/span>\r\n\r\n<\/div>\r\nA\u00a0[pb_glossary id=\"2520\"]Punnett square[\/pb_glossary]<\/strong> is a chart that allows you to easily determine the expected ratios of possible genotypes in the offspring of two parents. You can see a hypothetical example in Figure 5.13.3. In this case, the gene is autosomal, and both parents are heterozygotes (Aa)<\/em>\u00a0for the gene. Half of the gametes produced by each parent will have the\u00a0A<\/em>\u00a0allele, and half will have the\u00a0a<\/em> allele. That's because the two\u00a0alleles\u00a0are on homologous chromosomes, which always separate and go to separate gametes during\u00a0meiosis. The alleles in the gametes from each parent are written down the side and across the top of the Punnett square. Filling in the\u00a0cells\u00a0of the Punnett square gives the possible genotypes of their children. It also shows the most likely ratios of the genotypes, which in this case is 25 per cent\u00a0AA,<\/em> 50 per cent\u00a0Aa,<\/em> and 25 per cent\u00a0aa.<\/em>\r\n\r\n[caption id=\"attachment_2521\" align=\"aligncenter\" width=\"816\"] Figure 5.13.3 A Punnett square shows the most likely proportions of offspring by genotype for a particular mating type.<\/em>[\/caption]\r\n\r\n\r\n\r\nA Punnett square can also be used to show how the X and Y chromosomes are passed from parents to their children. This is illustrated in the Punnett square in Figure 5.13.4<\/span>. It may help you understand the inheritance pattern of sex-linked traits.<\/span>\r\n\r\n[caption id=\"attachment_2522\" align=\"aligncenter\" width=\"295\"] Figure 5.13.4 Inheritance of Sex Chromosomes. Mothers pass only X chromosomes to their children. Fathers always pass their X chromosome to their daughters, and their Y chromosome to their sons. Can you explain why fathers always determine the sex of the offspring?<\/em>[\/caption]\r\n\r\n<\/div>\r\n\r\n\r\nHere's how to fill out a Punnett Square:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=prkHKjfUmMs&t=\r\nLearn Biology: How to Draw a Punnett Square, mahalodotcom, 2011.<\/p>\r\nTry out this Punnett Square:\r\n\r\n[h5p id=\"507\"]\r\n
Autosomal Mendelian Traits in Humans<\/h1>\r\n<\/div>\r\nNot many human autosomal traits are controlled by a single gene with two\u00a0alleles, but they are a good starting point for understanding human heredity. As discussed in the beginning of this concept, most forms of albinism in humans have\u00a0a Mendelian inheritance pattern.\u00a0Albinism\u00a0is usually controlled by a single autosomal gene with two alleles. The\u00a0allele\u00a0for normal pigmentation (let's call it\u00a0R<\/em>) is dominant to the\u00a0allele\u00a0for albinism (r<\/em>). Individuals with either an\u00a0RR<\/em>\u00a0or\u00a0Rr\u00a0<\/em>genotype will not have albinism, because the\u00a0R<\/em>\u00a0allele\u00a0is dominant over the recessive\u00a0r<\/em>\u00a0allele.\r\n\r\nHowever,\u00a0consider what happens if two individuals with the\u00a0Rr<\/em>\u00a0genotype reproduce with each other. The outcome\u00a0would be\u00a0similar to\u00a0the example shown in the Punnett square\u00a0above\u00a0for two hypothetical\u00a0Aa<\/em>\u00a0individuals.\u00a0Their possible\u00a0offspring\u00a0could be\u00a0RR<\/em>\u00a0(normal pigmentation),\u00a0Rr<\/em>\u00a0(normal pigmentation), or\u00a0rr<\/em>\u00a0(albinism). This explains why a child with albinism (rr<\/em>), can have two parents that do not have albinism. Both unaffected parents must be a carrier of the recessive\u00a0r<\/em>\u00a0allele, but they also have a dominant\u00a0R <\/em>allele that prevents them from having the condition themselves.\r\n\r\nSome other human traits that\u00a0have a\u00a0Mendelian inheritance pattern\u00a0are Huntington's disease and\u00a0wet\u00a0versus\u00a0dry ear wax. You may have heard about other human traits that were\u00a0previously<\/em>\u00a0thought to be Mendelian,\u00a0such as dimples, a widow's peak hairline, hitchiker's thumb, and the ability to roll your tongue. As science has progressed, it is now understood that these are not actually Mendelian traits. In fact, most human traits are actually controlled by multiple genes, or otherwise have more than two alleles,\u00a0which means they\u00a0do not have\u00a0a\u00a0simple Mendelian inheritance pattern.\r\n\r\nX-Linked Mendelian Traits in Humans<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_2525\" align=\"alignright\" width=\"366\"] Figure 5.13.5 This circle of colours containing the number 74 is part of the Ishihara colour blindness test.<\/a><\/em>[\/caption]\r\n\r\nBecause males have just one X chromosome, they have only one allele for any X-linked trait. Therefore, a recessive X-linked allele is always expressed in males. Because females have two X chromosomes, they have two alleles for any X-linked trait. Therefore, they must inherit two copies of the recessive allele to express an X-linked recessive trait. This explains why X-linked recessive traits are less common in females than males, and why they show a different pattern of inheritance than autosomal traits.\r\n\r\n[caption id=\"attachment_2527\" align=\"alignleft\" width=\"334\"] Figure 5.13.6 Heredity implications of an X-linked recessive gene carried by the mother. <\/em>[\/caption]\r\n\r\nAn example of a recessive X-linked trait is red-green colour blindness. People with this trait cannot distinguish between the colours red and green. More than one recessive gene on the X chromosome codes for this trait, which is fairly common in males, but relatively rare in females. Figure 5.13.6 shows a simple pedigree for this trait. A female with one of the recessive alleles for the trait does not have the trait herself, but can pass it on to her children. In this case, she is called a carrier of the trait. Half of any sons she has can be expected to have the trait, because there is a 50 per cent chance that they will inherit the X chromosome with the colour-blindness allele. Having only one X chromosome, the recessive allele will be expressed in the sons who inherit it. However, as long as the father is not affected, none of the woman's daughters will have the trait. The daughters have a 50 per cent chance of inheriting the X chromosome with the colour-blindness allele, but it won't be expressed because it is recessive to the normal allele they inherit from their father.\r\n\r\n[caption id=\"attachment_2529\" align=\"alignright\" width=\"282\"] Figure 5.13.7 Queen Victoria carried hemophilia and she passed the hemophilia allele to two of her daughters and one of her sons. This portrait of her was painted in the 1840s.<\/em>[\/caption]\r\n\r\nAnother example of a recessive X-linked Mendelian trait is hemophilia, which is a disorder characterized by the blood's inability to clot normally. England's Queen Victoria (pictured in Figure 5.13.7) carried the disorder. Two of her five daughters inherited the hemophilia allele from their mother and were carriers. When they married royalty in other European countries, they spread the allele across Europe, including to the royal families of Spain, Germany, and Russia. Victoria's son Prince Leopold also inherited the hemophilia allele from his mother, and he actually suffered from the disease. Understandably, hemophilia was once popularly called \"the royal disease.\"\r\n\r\n\r\n \r\n\r\nFeature: My\u00a0Human Body<\/span>.\r\n\r\n<\/div>\r\nAre you colour blind, or do you think you might be? If you inherited this X-linked recessive disorder, a world without clear differences between certain colours seems normal to you. It's all you have ever known! Some people who are colour blind are not even aware of it. Simple tests have been devised to determine whether a person is colour blind, and to what degree. An example of such a test is pictured in Figure 5.13.5. What do you see when you look at this circle? Can you clearly perceive the number 74? If so, you probably have normal red-green colour vision. If you cannot see the number, you may have red-green colour blindness.\r\n\r\n[caption id=\"attachment_2530\" align=\"aligncenter\" width=\"484\"] Figure 5.13.8 Perception of colours comparison.<\/em>[\/caption]\r\n\r\nBeing colour blind can cause a number of problems. These may range from minor frustrations to outright dangers. Here are a few examples:\r\n\r\n \t- If you are colour blind, it may be difficult to colour-coordinate clothing and furnishings. You may end up wearing colour combinations that people with normal colour vision think are odd or clashing.<\/li>\r\n \t
- Many LED indicator lights are red or green.\u00a0Power strips and electronic devices, for example, may have indicator lights to show whether they are on (green) or off (red).<\/li>\r\n \t
- Test strips for pH, hard water, swimming pool chemicals, and other common tests are also often colour coded. Litmus paper for testing pH, for example, turns red in the presence of an acid, but if you are colour blind, you may not be able to read the test result.<\/li>\r\n \t
- Do you like your steak well done? If you are colour blind, you may not be able to tell if the meat is still undercooked (red) or grilled just right. You also may not be able to distinguish ripe (red) from unripe (green) fruits and vegetables, such as tomatoes. And some foods, such as dark green spinach, may look more like mud than food, making them totally unappetizing.<\/li>\r\n \t
- Weather maps often are colour coded. Is that rain (green) in your forecast, or a wintry mix of sleet and freezing rain (pink or red)? If you can't tell the difference, you may go out on the roads when you shouldn't, putting yourself in danger.<\/li>\r\n \t
- Being able to distinguish red from green traffic lights may be a matter of life or death. This can be very difficult for someone with red-green colour blindness. In some countries, people with this vision defect are not allowed to drive.<\/li>\r\n<\/ul>\r\n[h5p id=\"508\"]\r\n\r\nFigure 5.13.9\u00a0 Examples of challenges faced by those who are colour blind<\/em>\r\n\r\n
\r\n5.13 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"2515\"]Mendelian inheritance[\/pb_glossary] refers to the inheritance of traits controlled by a single [pb_glossary id=\"5521\"]gene[\/pb_glossary] with two [pb_glossary id=\"5449\"]alleles[\/pb_glossary], one of which may be completely dominant to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on [pb_glossary id=\"2112\"]autosomes[\/pb_glossary], or by genes on [pb_glossary id=\"2125\"]sex chromosomes[\/pb_glossary].<\/li>\r\n \t
- Two tools for studying inheritance are [pb_glossary id=\"2519\"]pedigrees[\/pb_glossary] and\u00a0[pb_glossary id=\"2520\"]Punnett squares[\/pb_glossary]. A pedigree is a chart that shows how a trait is passed from generation to generation within a family. A Punnett square is a chart that shows the expected ratios of possible [pb_glossary id=\"6039\"]genotypes[\/pb_glossary] in the offspring of two parents.<\/li>\r\n \t
- Examples of human autosomal Mendelian traits include albinism and Huntington's disease. Examples of human X-linked traits include red-green colour blindness and hemophilia.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Define genetic traits and Mendelian inheritance.<\/li>\r\n \t
- [h5p id=\"509\"]<\/li>\r\n \t
- Explain why autosomal and X-linked Mendelian traits have different patterns of inheritance.<\/li>\r\n \t
- Identify examples of human autosomal and X-linked Mendelian traits.<\/li>\r\n \t
- Imagine a hypothetical human gene that has two alleles,Q<\/em>and\u00a0q<\/em>.\u00a0Q<\/em>\u00a0is dominant to\u00a0q<\/em>\u00a0and the inheritance of this gene is Mendelian. Answer the following questions about this gene.\r\n
\r\n \t- If a woman has the genotype\u00a0Q q\u00a0<\/em>and her husband has the genotype\u00a0QQ<\/em>, list each of their possible gametes. What proportion of their gametes will have each allele?<\/li>\r\n \t
- What are the likely proportions of their offspring beingQQ<\/em>,Qq<\/em>, or\u00a0qq<\/em>?<\/li>\r\n \t
- Is this an autosomal trait or an X-linked trait? How do you know?<\/li>\r\n \t
- What are the chances of their offspring exhibiting the dominant\u00a0Q\u00a0<\/em>trait? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t
- Explain why fathers always pass their X chromosome down to their daughters.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=emb_logo\r\nPunnett Squares and Sex-Linked Traits, Amoeba Sisters, 2015.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4\r\n
Pedigrees, Amoeba Sisters, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=veB31XmUQm8\r\n
Secrets of the X chromosome - Robin Ball, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.13.1<\/strong>\r\n\r\nAlbino_baby_by_Felipe_Fernandes<\/a>\u00a0by Felipe Fernandes<\/a> on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0) license.\r\n\r\nFigure 5.13.2<\/strong>\r\n\r\nPedigree_Chart2.svg<\/a> by Jerome Walker on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Derivative work of original image<\/a>\u00a0created by\u00a0GAThrawn22<\/a>)\r\n\r\nFigure 5.13.3<\/strong>\r\n\r\nPunnett square by Christine Miller is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.4<\/strong>\r\n\r\nInheritance of Sex Chromosomes<\/a> by CK-12 Foundation<\/a> is used under a CC BY-NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 5.13.5<\/strong>\r\n\r\nRed-Green Colour Blindness<\/a> by Unknown author on Wikimedia is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\u00a0(Original believed to be by Shinobu Ishihara<\/a>)\r\n\r\nFigure 5.13.6<\/strong>\r\n\r\nXlinkRecessive<\/a> by US\u00a0National Institutes of Health<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.7<\/strong>\r\n\r\nThe_Young_Queen_Victoria (painted portrait<\/a> by Franz Xaver Winterhalter<\/a> (photograph from the Osborne House, Isle of Wight) on Wikimedia Commoons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.8<\/strong>\r\n\r\nDeuteranopia\/ Figure 9.10<\/a>\u00a0by Web Style Guide<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 5.13.9<\/strong>\r\n\r\n \t- LED traffic light<\/a> by Bidgee<\/a> on Wikimedia <\/i>is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.<\/li>\r\n \t
- Universal indicator paper<\/a> by Bordercolliez<\/a> on Wikimedia <\/em>is used under a CC0 1.0<\/a>\r\nPublic Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en)<\/li>\r\n \t
- Photo tags: Fruit tomatoes food fruits and vegetables fresh<\/a> by InspiredImages<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n \t
- Simple Control with Indicator LIghts<\/a> by Sam D. Wilbur<\/a> on Wikimedia is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/li>\r\n \t
- Photo tags: Feet socks checkered striped pants colorful color<\/a> by Suppenkasper<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\n
References<\/h2>\r\n
Amoeba Sisters. (2015, January 23).\u00a0 Punnett squares and sex-linked traits. YouTube. https:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=youtu.be<\/p>\r\n
Amoeba Sisters. (2017, February 8). Pedigrees. YouTube. https:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4&feature=youtu.be<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 3 Inherited traits of sex chromosomes [digital image]. In CK-12 College Human Biology\u00a0<\/em>(Section 5.12) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/5.12\/<\/p>\r\nmahalodotcom. (2011, January 14). Learn biology: How to draw a punnett square. YouTube. https:\/\/www.youtube.com\/watch?v=prkHKjfUmMs&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 18). Secrets of the X chromosome - Robin Ball. YouTube. https:\/\/www.youtube.com\/watch?v=veB31XmUQm8&feature=youtu.be<\/span><\/p>\r\nWikipedia contributors. (2020, June 26). Albinism in humans. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Albinism_in_humans&oldid=964622728<\/p>\r\nWikipedia contributors. (2020, June 29). Gregor Mendel. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Gregor_Mendel&oldid=965090119<\/p>\r\nWikipedia contributors. (2020, June 17). Ishihara test. In\u00a0Wikipedia. <\/i>https:\/\/en.wikipedia.org\/w\/index.php?title=Ishihara_test&oldid=963014774<\/p>","rendered":"
<\/p>\nFigure 5.13.1 Like mother, like son.<\/em><\/figcaption><\/figure>\n\nAlbinism<\/h1>\n<\/div>\n
This child has much lighter skin and\u00a0hair\u00a0than his parents. He has a condition called albinism<\/a>, which results from a\u00a0lack of\u00a0the\u00a0pigment melanin in the\u00a0skin,\u00a0hair, and\u00a0eyes. Although\u00a0he\u00a0looks<\/em>\u00a0different than his parents, albinism is actually a genetic trait.\u00a0Genetic traits<\/strong>\u00a0are characteristics that are encoded in\u00a0DNA. Most forms of albinism are recessive, which\u00a0is why\u00a0the child’s\u00a0parents were able to\u00a0pass\u00a0the trait to him without exhibiting the condition themselves. You will learn more about this type of inheritance\u00a0in this concept.\u00a0Albinism is\u00a0one of the few human traits that actually has a simple inheritance pattern,\u00a0similar to\u00a0the traits that Gregor\u00a0Mendel<\/a>\u00a0studied in\u00a0pea plants. The way these traits are inherited by offspring from their parents is called Mendelian inheritance<\/a>.<\/p>\n\nWhat Is Mendelian Inheritance?<\/h1>\n<\/div>\n
Mendelian inheritance<\/strong>\u00a0refers to the inheritance of traits controlled by a single gene with two\u00a0alleles<\/a>, one of which may be completely dominant<\/a> to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on autosome<\/a>s, or by genes on sex\u00a0chromosomes<\/a>.<\/p>\n\n- Autosomal traits<\/strong>\u00a0are controlled by genes on one of the 22 pairs of human autosomes<\/a>. Autosomes are all the\u00a0chromosomes\u00a0except the X or Y chromosome, and they do not differ between males and females, so autosomal traits are inherited in the same way, regardless of the sex of the parent or offspring.<\/li>\n
- Traits controlled by genes on the sex\u00a0chromosomes\u00a0are called\u00a0sex-linked traits<\/a>.<\/strong>\u00a0Because of the small size of the Y chromosome, most sex-linked traits are controlled by genes on the X chromosome. These traits are called\u00a0X-linked traits<\/a><\/strong>. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits, because males have just one X chromosome. In addition, males always inherit their X chromosome from their mother, and they pass on their X chromosome to all of their daughters, but none of their sons.<\/li>\n<\/ul>\n\n
Studying Inheritance Patterns<\/h1>\n<\/div>\n
There are two very useful tools for studying how traits are passed from one generation to the next. One tool is a\u00a0pedigree, and the other is a Punnett square.<\/p>\n
Pedigree<\/h2>\n
The chart below (Figure 5.13.2) is called a pedigree<\/a><\/strong>. A pedigree shows how a trait is passed from generation to generation within a family.\u00a0A pedigree can show, for example, whether a Mendelian trait is an autosomal<\/a> or X-linked<\/a> trait. It can also be used to infer the genotype of different members of the family.<\/p>\nThe trait represented by\u00a0this\u00a0chart is a hypothetical autosomal trait controlled by a dominant allele. At the top of the pedigree, you can see symbols representing a married couple. The husband\u00a0has<\/em> the trait (affected male), but the wife does not (unaffected female). The next row of the pedigree shows the couple’s children, as well as the spouses of three of the children. For example, the first child on the left is an affected male married to an unaffected female. The third row of the pedigree shows the next generation (the grandchildren of the couple at the top of the pedigree). One child in this generation \u2014 the affected female on the left \u2014 is the sibling of an unaffected male.<\/p>\nFigure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em><\/figcaption><\/figure>\n
Studying Inheritance Patterns<\/h1>\r\n<\/div>\r\nThere are two very useful tools for studying how traits are passed from one generation to the next. One tool is a\u00a0pedigree, and the other is a Punnett square.\r\nPedigree<\/h2>\r\nThe chart below (Figure 5.13.2) is called a [pb_glossary id=\"2519\"]pedigree[\/pb_glossary]<\/strong>. A pedigree shows how a trait is passed from generation to generation within a family.\u00a0A pedigree can show, for example, whether a Mendelian trait is an [pb_glossary id=\"2112\"]autosomal[\/pb_glossary] or [pb_glossary id=\"2517\"]X-linked[\/pb_glossary] trait. It can also be used to infer the genotype of different members of the family.\r\n\r\nThe trait represented by\u00a0this\u00a0chart is a hypothetical autosomal trait controlled by a dominant allele. At the top of the pedigree, you can see symbols representing a married couple. The husband\u00a0has<\/em> the trait (affected male), but the wife does not (unaffected female). The next row of the pedigree shows the couple's children, as well as the spouses of three of the children. For example, the first child on the left is an affected male married to an unaffected female. The third row of the pedigree shows the next generation (the grandchildren of the couple at the top of the pedigree). One child in this generation \u2014 the affected female on the left \u2014 is the sibling of an unaffected male.\r\n\r\n[caption id=\"attachment_2518\" align=\"aligncenter\" width=\"666\"] Figure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em>[\/caption]\r\n\r\n\r\n\r\nPunnett Square<\/span>\r\n\r\n<\/div>\r\nA\u00a0[pb_glossary id=\"2520\"]Punnett square[\/pb_glossary]<\/strong> is a chart that allows you to easily determine the expected ratios of possible genotypes in the offspring of two parents. You can see a hypothetical example in Figure 5.13.3. In this case, the gene is autosomal, and both parents are heterozygotes (Aa)<\/em>\u00a0for the gene. Half of the gametes produced by each parent will have the\u00a0A<\/em>\u00a0allele, and half will have the\u00a0a<\/em> allele. That's because the two\u00a0alleles\u00a0are on homologous chromosomes, which always separate and go to separate gametes during\u00a0meiosis. The alleles in the gametes from each parent are written down the side and across the top of the Punnett square. Filling in the\u00a0cells\u00a0of the Punnett square gives the possible genotypes of their children. It also shows the most likely ratios of the genotypes, which in this case is 25 per cent\u00a0AA,<\/em> 50 per cent\u00a0Aa,<\/em> and 25 per cent\u00a0aa.<\/em>\r\n\r\n[caption id=\"attachment_2521\" align=\"aligncenter\" width=\"816\"] Figure 5.13.3 A Punnett square shows the most likely proportions of offspring by genotype for a particular mating type.<\/em>[\/caption]\r\n\r\n\r\n\r\nA Punnett square can also be used to show how the X and Y chromosomes are passed from parents to their children. This is illustrated in the Punnett square in Figure 5.13.4<\/span>. It may help you understand the inheritance pattern of sex-linked traits.<\/span>\r\n\r\n[caption id=\"attachment_2522\" align=\"aligncenter\" width=\"295\"] Figure 5.13.4 Inheritance of Sex Chromosomes. Mothers pass only X chromosomes to their children. Fathers always pass their X chromosome to their daughters, and their Y chromosome to their sons. Can you explain why fathers always determine the sex of the offspring?<\/em>[\/caption]\r\n\r\n<\/div>\r\n\r\n\r\nHere's how to fill out a Punnett Square:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=prkHKjfUmMs&t=\r\nLearn Biology: How to Draw a Punnett Square, mahalodotcom, 2011.<\/p>\r\nTry out this Punnett Square:\r\n\r\n[h5p id=\"507\"]\r\n
Autosomal Mendelian Traits in Humans<\/h1>\r\n<\/div>\r\nNot many human autosomal traits are controlled by a single gene with two\u00a0alleles, but they are a good starting point for understanding human heredity. As discussed in the beginning of this concept, most forms of albinism in humans have\u00a0a Mendelian inheritance pattern.\u00a0Albinism\u00a0is usually controlled by a single autosomal gene with two alleles. The\u00a0allele\u00a0for normal pigmentation (let's call it\u00a0R<\/em>) is dominant to the\u00a0allele\u00a0for albinism (r<\/em>). Individuals with either an\u00a0RR<\/em>\u00a0or\u00a0Rr\u00a0<\/em>genotype will not have albinism, because the\u00a0R<\/em>\u00a0allele\u00a0is dominant over the recessive\u00a0r<\/em>\u00a0allele.\r\n\r\nHowever,\u00a0consider what happens if two individuals with the\u00a0Rr<\/em>\u00a0genotype reproduce with each other. The outcome\u00a0would be\u00a0similar to\u00a0the example shown in the Punnett square\u00a0above\u00a0for two hypothetical\u00a0Aa<\/em>\u00a0individuals.\u00a0Their possible\u00a0offspring\u00a0could be\u00a0RR<\/em>\u00a0(normal pigmentation),\u00a0Rr<\/em>\u00a0(normal pigmentation), or\u00a0rr<\/em>\u00a0(albinism). This explains why a child with albinism (rr<\/em>), can have two parents that do not have albinism. Both unaffected parents must be a carrier of the recessive\u00a0r<\/em>\u00a0allele, but they also have a dominant\u00a0R <\/em>allele that prevents them from having the condition themselves.\r\n\r\nSome other human traits that\u00a0have a\u00a0Mendelian inheritance pattern\u00a0are Huntington's disease and\u00a0wet\u00a0versus\u00a0dry ear wax. You may have heard about other human traits that were\u00a0previously<\/em>\u00a0thought to be Mendelian,\u00a0such as dimples, a widow's peak hairline, hitchiker's thumb, and the ability to roll your tongue. As science has progressed, it is now understood that these are not actually Mendelian traits. In fact, most human traits are actually controlled by multiple genes, or otherwise have more than two alleles,\u00a0which means they\u00a0do not have\u00a0a\u00a0simple Mendelian inheritance pattern.\r\n\r\nX-Linked Mendelian Traits in Humans<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_2525\" align=\"alignright\" width=\"366\"] Figure 5.13.5 This circle of colours containing the number 74 is part of the Ishihara colour blindness test.<\/a><\/em>[\/caption]\r\n\r\nBecause males have just one X chromosome, they have only one allele for any X-linked trait. Therefore, a recessive X-linked allele is always expressed in males. Because females have two X chromosomes, they have two alleles for any X-linked trait. Therefore, they must inherit two copies of the recessive allele to express an X-linked recessive trait. This explains why X-linked recessive traits are less common in females than males, and why they show a different pattern of inheritance than autosomal traits.\r\n\r\n[caption id=\"attachment_2527\" align=\"alignleft\" width=\"334\"] Figure 5.13.6 Heredity implications of an X-linked recessive gene carried by the mother. <\/em>[\/caption]\r\n\r\nAn example of a recessive X-linked trait is red-green colour blindness. People with this trait cannot distinguish between the colours red and green. More than one recessive gene on the X chromosome codes for this trait, which is fairly common in males, but relatively rare in females. Figure 5.13.6 shows a simple pedigree for this trait. A female with one of the recessive alleles for the trait does not have the trait herself, but can pass it on to her children. In this case, she is called a carrier of the trait. Half of any sons she has can be expected to have the trait, because there is a 50 per cent chance that they will inherit the X chromosome with the colour-blindness allele. Having only one X chromosome, the recessive allele will be expressed in the sons who inherit it. However, as long as the father is not affected, none of the woman's daughters will have the trait. The daughters have a 50 per cent chance of inheriting the X chromosome with the colour-blindness allele, but it won't be expressed because it is recessive to the normal allele they inherit from their father.\r\n\r\n[caption id=\"attachment_2529\" align=\"alignright\" width=\"282\"] Figure 5.13.7 Queen Victoria carried hemophilia and she passed the hemophilia allele to two of her daughters and one of her sons. This portrait of her was painted in the 1840s.<\/em>[\/caption]\r\n\r\nAnother example of a recessive X-linked Mendelian trait is hemophilia, which is a disorder characterized by the blood's inability to clot normally. England's Queen Victoria (pictured in Figure 5.13.7) carried the disorder. Two of her five daughters inherited the hemophilia allele from their mother and were carriers. When they married royalty in other European countries, they spread the allele across Europe, including to the royal families of Spain, Germany, and Russia. Victoria's son Prince Leopold also inherited the hemophilia allele from his mother, and he actually suffered from the disease. Understandably, hemophilia was once popularly called \"the royal disease.\"\r\n\r\n\r\n \r\n\r\nFeature: My\u00a0Human Body<\/span>.\r\n\r\n<\/div>\r\nAre you colour blind, or do you think you might be? If you inherited this X-linked recessive disorder, a world without clear differences between certain colours seems normal to you. It's all you have ever known! Some people who are colour blind are not even aware of it. Simple tests have been devised to determine whether a person is colour blind, and to what degree. An example of such a test is pictured in Figure 5.13.5. What do you see when you look at this circle? Can you clearly perceive the number 74? If so, you probably have normal red-green colour vision. If you cannot see the number, you may have red-green colour blindness.\r\n\r\n[caption id=\"attachment_2530\" align=\"aligncenter\" width=\"484\"] Figure 5.13.8 Perception of colours comparison.<\/em>[\/caption]\r\n\r\nBeing colour blind can cause a number of problems. These may range from minor frustrations to outright dangers. Here are a few examples:\r\n\r\n \t- If you are colour blind, it may be difficult to colour-coordinate clothing and furnishings. You may end up wearing colour combinations that people with normal colour vision think are odd or clashing.<\/li>\r\n \t
- Many LED indicator lights are red or green.\u00a0Power strips and electronic devices, for example, may have indicator lights to show whether they are on (green) or off (red).<\/li>\r\n \t
- Test strips for pH, hard water, swimming pool chemicals, and other common tests are also often colour coded. Litmus paper for testing pH, for example, turns red in the presence of an acid, but if you are colour blind, you may not be able to read the test result.<\/li>\r\n \t
- Do you like your steak well done? If you are colour blind, you may not be able to tell if the meat is still undercooked (red) or grilled just right. You also may not be able to distinguish ripe (red) from unripe (green) fruits and vegetables, such as tomatoes. And some foods, such as dark green spinach, may look more like mud than food, making them totally unappetizing.<\/li>\r\n \t
- Weather maps often are colour coded. Is that rain (green) in your forecast, or a wintry mix of sleet and freezing rain (pink or red)? If you can't tell the difference, you may go out on the roads when you shouldn't, putting yourself in danger.<\/li>\r\n \t
- Being able to distinguish red from green traffic lights may be a matter of life or death. This can be very difficult for someone with red-green colour blindness. In some countries, people with this vision defect are not allowed to drive.<\/li>\r\n<\/ul>\r\n[h5p id=\"508\"]\r\n\r\nFigure 5.13.9\u00a0 Examples of challenges faced by those who are colour blind<\/em>\r\n\r\n
\r\n5.13 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"2515\"]Mendelian inheritance[\/pb_glossary] refers to the inheritance of traits controlled by a single [pb_glossary id=\"5521\"]gene[\/pb_glossary] with two [pb_glossary id=\"5449\"]alleles[\/pb_glossary], one of which may be completely dominant to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on [pb_glossary id=\"2112\"]autosomes[\/pb_glossary], or by genes on [pb_glossary id=\"2125\"]sex chromosomes[\/pb_glossary].<\/li>\r\n \t
- Two tools for studying inheritance are [pb_glossary id=\"2519\"]pedigrees[\/pb_glossary] and\u00a0[pb_glossary id=\"2520\"]Punnett squares[\/pb_glossary]. A pedigree is a chart that shows how a trait is passed from generation to generation within a family. A Punnett square is a chart that shows the expected ratios of possible [pb_glossary id=\"6039\"]genotypes[\/pb_glossary] in the offspring of two parents.<\/li>\r\n \t
- Examples of human autosomal Mendelian traits include albinism and Huntington's disease. Examples of human X-linked traits include red-green colour blindness and hemophilia.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Define genetic traits and Mendelian inheritance.<\/li>\r\n \t
- [h5p id=\"509\"]<\/li>\r\n \t
- Explain why autosomal and X-linked Mendelian traits have different patterns of inheritance.<\/li>\r\n \t
- Identify examples of human autosomal and X-linked Mendelian traits.<\/li>\r\n \t
- Imagine a hypothetical human gene that has two alleles,Q<\/em>and\u00a0q<\/em>.\u00a0Q<\/em>\u00a0is dominant to\u00a0q<\/em>\u00a0and the inheritance of this gene is Mendelian. Answer the following questions about this gene.\r\n
\r\n \t- If a woman has the genotype\u00a0Q q\u00a0<\/em>and her husband has the genotype\u00a0QQ<\/em>, list each of their possible gametes. What proportion of their gametes will have each allele?<\/li>\r\n \t
- What are the likely proportions of their offspring beingQQ<\/em>,Qq<\/em>, or\u00a0qq<\/em>?<\/li>\r\n \t
- Is this an autosomal trait or an X-linked trait? How do you know?<\/li>\r\n \t
- What are the chances of their offspring exhibiting the dominant\u00a0Q\u00a0<\/em>trait? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t
- Explain why fathers always pass their X chromosome down to their daughters.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=emb_logo\r\nPunnett Squares and Sex-Linked Traits, Amoeba Sisters, 2015.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4\r\n
Pedigrees, Amoeba Sisters, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=veB31XmUQm8\r\n
Secrets of the X chromosome - Robin Ball, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.13.1<\/strong>\r\n\r\nAlbino_baby_by_Felipe_Fernandes<\/a>\u00a0by Felipe Fernandes<\/a> on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0) license.\r\n\r\nFigure 5.13.2<\/strong>\r\n\r\nPedigree_Chart2.svg<\/a> by Jerome Walker on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Derivative work of original image<\/a>\u00a0created by\u00a0GAThrawn22<\/a>)\r\n\r\nFigure 5.13.3<\/strong>\r\n\r\nPunnett square by Christine Miller is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.4<\/strong>\r\n\r\nInheritance of Sex Chromosomes<\/a> by CK-12 Foundation<\/a> is used under a CC BY-NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 5.13.5<\/strong>\r\n\r\nRed-Green Colour Blindness<\/a> by Unknown author on Wikimedia is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\u00a0(Original believed to be by Shinobu Ishihara<\/a>)\r\n\r\nFigure 5.13.6<\/strong>\r\n\r\nXlinkRecessive<\/a> by US\u00a0National Institutes of Health<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.7<\/strong>\r\n\r\nThe_Young_Queen_Victoria (painted portrait<\/a> by Franz Xaver Winterhalter<\/a> (photograph from the Osborne House, Isle of Wight) on Wikimedia Commoons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.8<\/strong>\r\n\r\nDeuteranopia\/ Figure 9.10<\/a>\u00a0by Web Style Guide<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 5.13.9<\/strong>\r\n\r\n \t- LED traffic light<\/a> by Bidgee<\/a> on Wikimedia <\/i>is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.<\/li>\r\n \t
- Universal indicator paper<\/a> by Bordercolliez<\/a> on Wikimedia <\/em>is used under a CC0 1.0<\/a>\r\nPublic Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en)<\/li>\r\n \t
- Photo tags: Fruit tomatoes food fruits and vegetables fresh<\/a> by InspiredImages<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n \t
- Simple Control with Indicator LIghts<\/a> by Sam D. Wilbur<\/a> on Wikimedia is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/li>\r\n \t
- Photo tags: Feet socks checkered striped pants colorful color<\/a> by Suppenkasper<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\n
References<\/h2>\r\n
Amoeba Sisters. (2015, January 23).\u00a0 Punnett squares and sex-linked traits. YouTube. https:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=youtu.be<\/p>\r\n
Amoeba Sisters. (2017, February 8). Pedigrees. YouTube. https:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4&feature=youtu.be<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 3 Inherited traits of sex chromosomes [digital image]. In CK-12 College Human Biology\u00a0<\/em>(Section 5.12) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/5.12\/<\/p>\r\nmahalodotcom. (2011, January 14). Learn biology: How to draw a punnett square. YouTube. https:\/\/www.youtube.com\/watch?v=prkHKjfUmMs&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 18). Secrets of the X chromosome - Robin Ball. YouTube. https:\/\/www.youtube.com\/watch?v=veB31XmUQm8&feature=youtu.be<\/span><\/p>\r\nWikipedia contributors. (2020, June 26). Albinism in humans. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Albinism_in_humans&oldid=964622728<\/p>\r\nWikipedia contributors. (2020, June 29). Gregor Mendel. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Gregor_Mendel&oldid=965090119<\/p>\r\nWikipedia contributors. (2020, June 17). Ishihara test. In\u00a0Wikipedia. <\/i>https:\/\/en.wikipedia.org\/w\/index.php?title=Ishihara_test&oldid=963014774<\/p>","rendered":"
<\/p>\nFigure 5.13.1 Like mother, like son.<\/em><\/figcaption><\/figure>\n\nAlbinism<\/h1>\n<\/div>\n
This child has much lighter skin and\u00a0hair\u00a0than his parents. He has a condition called albinism<\/a>, which results from a\u00a0lack of\u00a0the\u00a0pigment melanin in the\u00a0skin,\u00a0hair, and\u00a0eyes. Although\u00a0he\u00a0looks<\/em>\u00a0different than his parents, albinism is actually a genetic trait.\u00a0Genetic traits<\/strong>\u00a0are characteristics that are encoded in\u00a0DNA. Most forms of albinism are recessive, which\u00a0is why\u00a0the child’s\u00a0parents were able to\u00a0pass\u00a0the trait to him without exhibiting the condition themselves. You will learn more about this type of inheritance\u00a0in this concept.\u00a0Albinism is\u00a0one of the few human traits that actually has a simple inheritance pattern,\u00a0similar to\u00a0the traits that Gregor\u00a0Mendel<\/a>\u00a0studied in\u00a0pea plants. The way these traits are inherited by offspring from their parents is called Mendelian inheritance<\/a>.<\/p>\n\nWhat Is Mendelian Inheritance?<\/h1>\n<\/div>\n
Mendelian inheritance<\/strong>\u00a0refers to the inheritance of traits controlled by a single gene with two\u00a0alleles<\/a>, one of which may be completely dominant<\/a> to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on autosome<\/a>s, or by genes on sex\u00a0chromosomes<\/a>.<\/p>\n\n- Autosomal traits<\/strong>\u00a0are controlled by genes on one of the 22 pairs of human autosomes<\/a>. Autosomes are all the\u00a0chromosomes\u00a0except the X or Y chromosome, and they do not differ between males and females, so autosomal traits are inherited in the same way, regardless of the sex of the parent or offspring.<\/li>\n
- Traits controlled by genes on the sex\u00a0chromosomes\u00a0are called\u00a0sex-linked traits<\/a>.<\/strong>\u00a0Because of the small size of the Y chromosome, most sex-linked traits are controlled by genes on the X chromosome. These traits are called\u00a0X-linked traits<\/a><\/strong>. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits, because males have just one X chromosome. In addition, males always inherit their X chromosome from their mother, and they pass on their X chromosome to all of their daughters, but none of their sons.<\/li>\n<\/ul>\n\n
Studying Inheritance Patterns<\/h1>\n<\/div>\n
There are two very useful tools for studying how traits are passed from one generation to the next. One tool is a\u00a0pedigree, and the other is a Punnett square.<\/p>\n
Pedigree<\/h2>\n
The chart below (Figure 5.13.2) is called a pedigree<\/a><\/strong>. A pedigree shows how a trait is passed from generation to generation within a family.\u00a0A pedigree can show, for example, whether a Mendelian trait is an autosomal<\/a> or X-linked<\/a> trait. It can also be used to infer the genotype of different members of the family.<\/p>\nThe trait represented by\u00a0this\u00a0chart is a hypothetical autosomal trait controlled by a dominant allele. At the top of the pedigree, you can see symbols representing a married couple. The husband\u00a0has<\/em> the trait (affected male), but the wife does not (unaffected female). The next row of the pedigree shows the couple’s children, as well as the spouses of three of the children. For example, the first child on the left is an affected male married to an unaffected female. The third row of the pedigree shows the next generation (the grandchildren of the couple at the top of the pedigree). One child in this generation \u2014 the affected female on the left \u2014 is the sibling of an unaffected male.<\/p>\nFigure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em><\/figcaption><\/figure>\n
Figure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em>[\/caption]\r\n\r\n Figure 5.13.3 A Punnett square shows the most likely proportions of offspring by genotype for a particular mating type.<\/em>[\/caption]\r\n\r\n Figure 5.13.4 Inheritance of Sex Chromosomes. Mothers pass only X chromosomes to their children. Fathers always pass their X chromosome to their daughters, and their Y chromosome to their sons. Can you explain why fathers always determine the sex of the offspring?<\/em>[\/caption]\r\n\r\n<\/div>\r\nLearn Biology: How to Draw a Punnett Square, mahalodotcom, 2011.<\/p>\r\nTry out this Punnett Square:\r\n\r\n[h5p id=\"507\"]\r\n
Autosomal Mendelian Traits in Humans<\/h1>\r\n<\/div>\r\nNot many human autosomal traits are controlled by a single gene with two\u00a0alleles, but they are a good starting point for understanding human heredity. As discussed in the beginning of this concept, most forms of albinism in humans have\u00a0a Mendelian inheritance pattern.\u00a0Albinism\u00a0is usually controlled by a single autosomal gene with two alleles. The\u00a0allele\u00a0for normal pigmentation (let's call it\u00a0R<\/em>) is dominant to the\u00a0allele\u00a0for albinism (r<\/em>). Individuals with either an\u00a0RR<\/em>\u00a0or\u00a0Rr\u00a0<\/em>genotype will not have albinism, because the\u00a0R<\/em>\u00a0allele\u00a0is dominant over the recessive\u00a0r<\/em>\u00a0allele.\r\n\r\nHowever,\u00a0consider what happens if two individuals with the\u00a0Rr<\/em>\u00a0genotype reproduce with each other. The outcome\u00a0would be\u00a0similar to\u00a0the example shown in the Punnett square\u00a0above\u00a0for two hypothetical\u00a0Aa<\/em>\u00a0individuals.\u00a0Their possible\u00a0offspring\u00a0could be\u00a0RR<\/em>\u00a0(normal pigmentation),\u00a0Rr<\/em>\u00a0(normal pigmentation), or\u00a0rr<\/em>\u00a0(albinism). This explains why a child with albinism (rr<\/em>), can have two parents that do not have albinism. Both unaffected parents must be a carrier of the recessive\u00a0r<\/em>\u00a0allele, but they also have a dominant\u00a0R <\/em>allele that prevents them from having the condition themselves.\r\n\r\nSome other human traits that\u00a0have a\u00a0Mendelian inheritance pattern\u00a0are Huntington's disease and\u00a0wet\u00a0versus\u00a0dry ear wax. You may have heard about other human traits that were\u00a0previously<\/em>\u00a0thought to be Mendelian,\u00a0such as dimples, a widow's peak hairline, hitchiker's thumb, and the ability to roll your tongue. As science has progressed, it is now understood that these are not actually Mendelian traits. In fact, most human traits are actually controlled by multiple genes, or otherwise have more than two alleles,\u00a0which means they\u00a0do not have\u00a0a\u00a0simple Mendelian inheritance pattern.\r\n\r\nX-Linked Mendelian Traits in Humans<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_2525\" align=\"alignright\" width=\"366\"] Figure 5.13.5 This circle of colours containing the number 74 is part of the Ishihara colour blindness test.<\/a><\/em>[\/caption]\r\n\r\nBecause males have just one X chromosome, they have only one allele for any X-linked trait. Therefore, a recessive X-linked allele is always expressed in males. Because females have two X chromosomes, they have two alleles for any X-linked trait. Therefore, they must inherit two copies of the recessive allele to express an X-linked recessive trait. This explains why X-linked recessive traits are less common in females than males, and why they show a different pattern of inheritance than autosomal traits.\r\n\r\n[caption id=\"attachment_2527\" align=\"alignleft\" width=\"334\"] Figure 5.13.6 Heredity implications of an X-linked recessive gene carried by the mother. <\/em>[\/caption]\r\n\r\nAn example of a recessive X-linked trait is red-green colour blindness. People with this trait cannot distinguish between the colours red and green. More than one recessive gene on the X chromosome codes for this trait, which is fairly common in males, but relatively rare in females. Figure 5.13.6 shows a simple pedigree for this trait. A female with one of the recessive alleles for the trait does not have the trait herself, but can pass it on to her children. In this case, she is called a carrier of the trait. Half of any sons she has can be expected to have the trait, because there is a 50 per cent chance that they will inherit the X chromosome with the colour-blindness allele. Having only one X chromosome, the recessive allele will be expressed in the sons who inherit it. However, as long as the father is not affected, none of the woman's daughters will have the trait. The daughters have a 50 per cent chance of inheriting the X chromosome with the colour-blindness allele, but it won't be expressed because it is recessive to the normal allele they inherit from their father.\r\n\r\n[caption id=\"attachment_2529\" align=\"alignright\" width=\"282\"] Figure 5.13.7 Queen Victoria carried hemophilia and she passed the hemophilia allele to two of her daughters and one of her sons. This portrait of her was painted in the 1840s.<\/em>[\/caption]\r\n\r\nAnother example of a recessive X-linked Mendelian trait is hemophilia, which is a disorder characterized by the blood's inability to clot normally. England's Queen Victoria (pictured in Figure 5.13.7) carried the disorder. Two of her five daughters inherited the hemophilia allele from their mother and were carriers. When they married royalty in other European countries, they spread the allele across Europe, including to the royal families of Spain, Germany, and Russia. Victoria's son Prince Leopold also inherited the hemophilia allele from his mother, and he actually suffered from the disease. Understandably, hemophilia was once popularly called \"the royal disease.\"\r\n\r\n\r\n \r\n\r\nFeature: My\u00a0Human Body<\/span>.\r\n\r\n<\/div>\r\nAre you colour blind, or do you think you might be? If you inherited this X-linked recessive disorder, a world without clear differences between certain colours seems normal to you. It's all you have ever known! Some people who are colour blind are not even aware of it. Simple tests have been devised to determine whether a person is colour blind, and to what degree. An example of such a test is pictured in Figure 5.13.5. What do you see when you look at this circle? Can you clearly perceive the number 74? If so, you probably have normal red-green colour vision. If you cannot see the number, you may have red-green colour blindness.\r\n\r\n[caption id=\"attachment_2530\" align=\"aligncenter\" width=\"484\"] Figure 5.13.8 Perception of colours comparison.<\/em>[\/caption]\r\n\r\nBeing colour blind can cause a number of problems. These may range from minor frustrations to outright dangers. Here are a few examples:\r\n\r\n \t- If you are colour blind, it may be difficult to colour-coordinate clothing and furnishings. You may end up wearing colour combinations that people with normal colour vision think are odd or clashing.<\/li>\r\n \t
- Many LED indicator lights are red or green.\u00a0Power strips and electronic devices, for example, may have indicator lights to show whether they are on (green) or off (red).<\/li>\r\n \t
- Test strips for pH, hard water, swimming pool chemicals, and other common tests are also often colour coded. Litmus paper for testing pH, for example, turns red in the presence of an acid, but if you are colour blind, you may not be able to read the test result.<\/li>\r\n \t
- Do you like your steak well done? If you are colour blind, you may not be able to tell if the meat is still undercooked (red) or grilled just right. You also may not be able to distinguish ripe (red) from unripe (green) fruits and vegetables, such as tomatoes. And some foods, such as dark green spinach, may look more like mud than food, making them totally unappetizing.<\/li>\r\n \t
- Weather maps often are colour coded. Is that rain (green) in your forecast, or a wintry mix of sleet and freezing rain (pink or red)? If you can't tell the difference, you may go out on the roads when you shouldn't, putting yourself in danger.<\/li>\r\n \t
- Being able to distinguish red from green traffic lights may be a matter of life or death. This can be very difficult for someone with red-green colour blindness. In some countries, people with this vision defect are not allowed to drive.<\/li>\r\n<\/ul>\r\n[h5p id=\"508\"]\r\n\r\nFigure 5.13.9\u00a0 Examples of challenges faced by those who are colour blind<\/em>\r\n\r\n
\r\n5.13 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"2515\"]Mendelian inheritance[\/pb_glossary] refers to the inheritance of traits controlled by a single [pb_glossary id=\"5521\"]gene[\/pb_glossary] with two [pb_glossary id=\"5449\"]alleles[\/pb_glossary], one of which may be completely dominant to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on [pb_glossary id=\"2112\"]autosomes[\/pb_glossary], or by genes on [pb_glossary id=\"2125\"]sex chromosomes[\/pb_glossary].<\/li>\r\n \t
- Two tools for studying inheritance are [pb_glossary id=\"2519\"]pedigrees[\/pb_glossary] and\u00a0[pb_glossary id=\"2520\"]Punnett squares[\/pb_glossary]. A pedigree is a chart that shows how a trait is passed from generation to generation within a family. A Punnett square is a chart that shows the expected ratios of possible [pb_glossary id=\"6039\"]genotypes[\/pb_glossary] in the offspring of two parents.<\/li>\r\n \t
- Examples of human autosomal Mendelian traits include albinism and Huntington's disease. Examples of human X-linked traits include red-green colour blindness and hemophilia.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Define genetic traits and Mendelian inheritance.<\/li>\r\n \t
- [h5p id=\"509\"]<\/li>\r\n \t
- Explain why autosomal and X-linked Mendelian traits have different patterns of inheritance.<\/li>\r\n \t
- Identify examples of human autosomal and X-linked Mendelian traits.<\/li>\r\n \t
- Imagine a hypothetical human gene that has two alleles,Q<\/em>and\u00a0q<\/em>.\u00a0Q<\/em>\u00a0is dominant to\u00a0q<\/em>\u00a0and the inheritance of this gene is Mendelian. Answer the following questions about this gene.\r\n
\r\n \t- If a woman has the genotype\u00a0Q q\u00a0<\/em>and her husband has the genotype\u00a0QQ<\/em>, list each of their possible gametes. What proportion of their gametes will have each allele?<\/li>\r\n \t
- What are the likely proportions of their offspring beingQQ<\/em>,Qq<\/em>, or\u00a0qq<\/em>?<\/li>\r\n \t
- Is this an autosomal trait or an X-linked trait? How do you know?<\/li>\r\n \t
- What are the chances of their offspring exhibiting the dominant\u00a0Q\u00a0<\/em>trait? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t
- Explain why fathers always pass their X chromosome down to their daughters.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=emb_logo\r\nPunnett Squares and Sex-Linked Traits, Amoeba Sisters, 2015.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4\r\n
Pedigrees, Amoeba Sisters, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=veB31XmUQm8\r\n
Secrets of the X chromosome - Robin Ball, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.13.1<\/strong>\r\n\r\nAlbino_baby_by_Felipe_Fernandes<\/a>\u00a0by Felipe Fernandes<\/a> on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0) license.\r\n\r\nFigure 5.13.2<\/strong>\r\n\r\nPedigree_Chart2.svg<\/a> by Jerome Walker on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Derivative work of original image<\/a>\u00a0created by\u00a0GAThrawn22<\/a>)\r\n\r\nFigure 5.13.3<\/strong>\r\n\r\nPunnett square by Christine Miller is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.4<\/strong>\r\n\r\nInheritance of Sex Chromosomes<\/a> by CK-12 Foundation<\/a> is used under a CC BY-NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 5.13.5<\/strong>\r\n\r\nRed-Green Colour Blindness<\/a> by Unknown author on Wikimedia is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\u00a0(Original believed to be by Shinobu Ishihara<\/a>)\r\n\r\nFigure 5.13.6<\/strong>\r\n\r\nXlinkRecessive<\/a> by US\u00a0National Institutes of Health<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.7<\/strong>\r\n\r\nThe_Young_Queen_Victoria (painted portrait<\/a> by Franz Xaver Winterhalter<\/a> (photograph from the Osborne House, Isle of Wight) on Wikimedia Commoons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.8<\/strong>\r\n\r\nDeuteranopia\/ Figure 9.10<\/a>\u00a0by Web Style Guide<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 5.13.9<\/strong>\r\n\r\n \t- LED traffic light<\/a> by Bidgee<\/a> on Wikimedia <\/i>is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.<\/li>\r\n \t
- Universal indicator paper<\/a> by Bordercolliez<\/a> on Wikimedia <\/em>is used under a CC0 1.0<\/a>\r\nPublic Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en)<\/li>\r\n \t
- Photo tags: Fruit tomatoes food fruits and vegetables fresh<\/a> by InspiredImages<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n \t
- Simple Control with Indicator LIghts<\/a> by Sam D. Wilbur<\/a> on Wikimedia is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/li>\r\n \t
- Photo tags: Feet socks checkered striped pants colorful color<\/a> by Suppenkasper<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\n
References<\/h2>\r\n
Amoeba Sisters. (2015, January 23).\u00a0 Punnett squares and sex-linked traits. YouTube. https:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=youtu.be<\/p>\r\n
Amoeba Sisters. (2017, February 8). Pedigrees. YouTube. https:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4&feature=youtu.be<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 3 Inherited traits of sex chromosomes [digital image]. In CK-12 College Human Biology\u00a0<\/em>(Section 5.12) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/5.12\/<\/p>\r\nmahalodotcom. (2011, January 14). Learn biology: How to draw a punnett square. YouTube. https:\/\/www.youtube.com\/watch?v=prkHKjfUmMs&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 18). Secrets of the X chromosome - Robin Ball. YouTube. https:\/\/www.youtube.com\/watch?v=veB31XmUQm8&feature=youtu.be<\/span><\/p>\r\nWikipedia contributors. (2020, June 26). Albinism in humans. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Albinism_in_humans&oldid=964622728<\/p>\r\nWikipedia contributors. (2020, June 29). Gregor Mendel. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Gregor_Mendel&oldid=965090119<\/p>\r\nWikipedia contributors. (2020, June 17). Ishihara test. In\u00a0Wikipedia. <\/i>https:\/\/en.wikipedia.org\/w\/index.php?title=Ishihara_test&oldid=963014774<\/p>","rendered":"
<\/p>\nFigure 5.13.1 Like mother, like son.<\/em><\/figcaption><\/figure>\n\nAlbinism<\/h1>\n<\/div>\n
This child has much lighter skin and\u00a0hair\u00a0than his parents. He has a condition called albinism<\/a>, which results from a\u00a0lack of\u00a0the\u00a0pigment melanin in the\u00a0skin,\u00a0hair, and\u00a0eyes. Although\u00a0he\u00a0looks<\/em>\u00a0different than his parents, albinism is actually a genetic trait.\u00a0Genetic traits<\/strong>\u00a0are characteristics that are encoded in\u00a0DNA. Most forms of albinism are recessive, which\u00a0is why\u00a0the child’s\u00a0parents were able to\u00a0pass\u00a0the trait to him without exhibiting the condition themselves. You will learn more about this type of inheritance\u00a0in this concept.\u00a0Albinism is\u00a0one of the few human traits that actually has a simple inheritance pattern,\u00a0similar to\u00a0the traits that Gregor\u00a0Mendel<\/a>\u00a0studied in\u00a0pea plants. The way these traits are inherited by offspring from their parents is called Mendelian inheritance<\/a>.<\/p>\n\nWhat Is Mendelian Inheritance?<\/h1>\n<\/div>\n
Mendelian inheritance<\/strong>\u00a0refers to the inheritance of traits controlled by a single gene with two\u00a0alleles<\/a>, one of which may be completely dominant<\/a> to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on autosome<\/a>s, or by genes on sex\u00a0chromosomes<\/a>.<\/p>\n\n- Autosomal traits<\/strong>\u00a0are controlled by genes on one of the 22 pairs of human autosomes<\/a>. Autosomes are all the\u00a0chromosomes\u00a0except the X or Y chromosome, and they do not differ between males and females, so autosomal traits are inherited in the same way, regardless of the sex of the parent or offspring.<\/li>\n
- Traits controlled by genes on the sex\u00a0chromosomes\u00a0are called\u00a0sex-linked traits<\/a>.<\/strong>\u00a0Because of the small size of the Y chromosome, most sex-linked traits are controlled by genes on the X chromosome. These traits are called\u00a0X-linked traits<\/a><\/strong>. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits, because males have just one X chromosome. In addition, males always inherit their X chromosome from their mother, and they pass on their X chromosome to all of their daughters, but none of their sons.<\/li>\n<\/ul>\n\n
Studying Inheritance Patterns<\/h1>\n<\/div>\n
There are two very useful tools for studying how traits are passed from one generation to the next. One tool is a\u00a0pedigree, and the other is a Punnett square.<\/p>\n
Pedigree<\/h2>\n
The chart below (Figure 5.13.2) is called a pedigree<\/a><\/strong>. A pedigree shows how a trait is passed from generation to generation within a family.\u00a0A pedigree can show, for example, whether a Mendelian trait is an autosomal<\/a> or X-linked<\/a> trait. It can also be used to infer the genotype of different members of the family.<\/p>\nThe trait represented by\u00a0this\u00a0chart is a hypothetical autosomal trait controlled by a dominant allele. At the top of the pedigree, you can see symbols representing a married couple. The husband\u00a0has<\/em> the trait (affected male), but the wife does not (unaffected female). The next row of the pedigree shows the couple’s children, as well as the spouses of three of the children. For example, the first child on the left is an affected male married to an unaffected female. The third row of the pedigree shows the next generation (the grandchildren of the couple at the top of the pedigree). One child in this generation \u2014 the affected female on the left \u2014 is the sibling of an unaffected male.<\/p>\nFigure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em><\/figcaption><\/figure>\n
X-Linked Mendelian Traits in Humans<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_2525\" align=\"alignright\" width=\"366\"] Figure 5.13.5 This circle of colours containing the number 74 is part of the Ishihara colour blindness test.<\/a><\/em>[\/caption]\r\n\r\nBecause males have just one X chromosome, they have only one allele for any X-linked trait. Therefore, a recessive X-linked allele is always expressed in males. Because females have two X chromosomes, they have two alleles for any X-linked trait. Therefore, they must inherit two copies of the recessive allele to express an X-linked recessive trait. This explains why X-linked recessive traits are less common in females than males, and why they show a different pattern of inheritance than autosomal traits.\r\n\r\n[caption id=\"attachment_2527\" align=\"alignleft\" width=\"334\"] Figure 5.13.6 Heredity implications of an X-linked recessive gene carried by the mother. <\/em>[\/caption]\r\n\r\nAn example of a recessive X-linked trait is red-green colour blindness. People with this trait cannot distinguish between the colours red and green. More than one recessive gene on the X chromosome codes for this trait, which is fairly common in males, but relatively rare in females. Figure 5.13.6 shows a simple pedigree for this trait. A female with one of the recessive alleles for the trait does not have the trait herself, but can pass it on to her children. In this case, she is called a carrier of the trait. Half of any sons she has can be expected to have the trait, because there is a 50 per cent chance that they will inherit the X chromosome with the colour-blindness allele. Having only one X chromosome, the recessive allele will be expressed in the sons who inherit it. However, as long as the father is not affected, none of the woman's daughters will have the trait. The daughters have a 50 per cent chance of inheriting the X chromosome with the colour-blindness allele, but it won't be expressed because it is recessive to the normal allele they inherit from their father.\r\n\r\n[caption id=\"attachment_2529\" align=\"alignright\" width=\"282\"] Figure 5.13.7 Queen Victoria carried hemophilia and she passed the hemophilia allele to two of her daughters and one of her sons. This portrait of her was painted in the 1840s.<\/em>[\/caption]\r\n\r\nAnother example of a recessive X-linked Mendelian trait is hemophilia, which is a disorder characterized by the blood's inability to clot normally. England's Queen Victoria (pictured in Figure 5.13.7) carried the disorder. Two of her five daughters inherited the hemophilia allele from their mother and were carriers. When they married royalty in other European countries, they spread the allele across Europe, including to the royal families of Spain, Germany, and Russia. Victoria's son Prince Leopold also inherited the hemophilia allele from his mother, and he actually suffered from the disease. Understandably, hemophilia was once popularly called \"the royal disease.\"\r\n\r\n\r\n \r\n\r\nFeature: My\u00a0Human Body<\/span>.\r\n\r\n<\/div>\r\nAre you colour blind, or do you think you might be? If you inherited this X-linked recessive disorder, a world without clear differences between certain colours seems normal to you. It's all you have ever known! Some people who are colour blind are not even aware of it. Simple tests have been devised to determine whether a person is colour blind, and to what degree. An example of such a test is pictured in Figure 5.13.5. What do you see when you look at this circle? Can you clearly perceive the number 74? If so, you probably have normal red-green colour vision. If you cannot see the number, you may have red-green colour blindness.\r\n\r\n[caption id=\"attachment_2530\" align=\"aligncenter\" width=\"484\"] Figure 5.13.8 Perception of colours comparison.<\/em>[\/caption]\r\n\r\nBeing colour blind can cause a number of problems. These may range from minor frustrations to outright dangers. Here are a few examples:\r\n\r\n \t- If you are colour blind, it may be difficult to colour-coordinate clothing and furnishings. You may end up wearing colour combinations that people with normal colour vision think are odd or clashing.<\/li>\r\n \t
- Many LED indicator lights are red or green.\u00a0Power strips and electronic devices, for example, may have indicator lights to show whether they are on (green) or off (red).<\/li>\r\n \t
- Test strips for pH, hard water, swimming pool chemicals, and other common tests are also often colour coded. Litmus paper for testing pH, for example, turns red in the presence of an acid, but if you are colour blind, you may not be able to read the test result.<\/li>\r\n \t
- Do you like your steak well done? If you are colour blind, you may not be able to tell if the meat is still undercooked (red) or grilled just right. You also may not be able to distinguish ripe (red) from unripe (green) fruits and vegetables, such as tomatoes. And some foods, such as dark green spinach, may look more like mud than food, making them totally unappetizing.<\/li>\r\n \t
- Weather maps often are colour coded. Is that rain (green) in your forecast, or a wintry mix of sleet and freezing rain (pink or red)? If you can't tell the difference, you may go out on the roads when you shouldn't, putting yourself in danger.<\/li>\r\n \t
- Being able to distinguish red from green traffic lights may be a matter of life or death. This can be very difficult for someone with red-green colour blindness. In some countries, people with this vision defect are not allowed to drive.<\/li>\r\n<\/ul>\r\n[h5p id=\"508\"]\r\n\r\nFigure 5.13.9\u00a0 Examples of challenges faced by those who are colour blind<\/em>\r\n\r\n
\r\n5.13 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"2515\"]Mendelian inheritance[\/pb_glossary] refers to the inheritance of traits controlled by a single [pb_glossary id=\"5521\"]gene[\/pb_glossary] with two [pb_glossary id=\"5449\"]alleles[\/pb_glossary], one of which may be completely dominant to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on [pb_glossary id=\"2112\"]autosomes[\/pb_glossary], or by genes on [pb_glossary id=\"2125\"]sex chromosomes[\/pb_glossary].<\/li>\r\n \t
- Two tools for studying inheritance are [pb_glossary id=\"2519\"]pedigrees[\/pb_glossary] and\u00a0[pb_glossary id=\"2520\"]Punnett squares[\/pb_glossary]. A pedigree is a chart that shows how a trait is passed from generation to generation within a family. A Punnett square is a chart that shows the expected ratios of possible [pb_glossary id=\"6039\"]genotypes[\/pb_glossary] in the offspring of two parents.<\/li>\r\n \t
- Examples of human autosomal Mendelian traits include albinism and Huntington's disease. Examples of human X-linked traits include red-green colour blindness and hemophilia.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Define genetic traits and Mendelian inheritance.<\/li>\r\n \t
- [h5p id=\"509\"]<\/li>\r\n \t
- Explain why autosomal and X-linked Mendelian traits have different patterns of inheritance.<\/li>\r\n \t
- Identify examples of human autosomal and X-linked Mendelian traits.<\/li>\r\n \t
- Imagine a hypothetical human gene that has two alleles,Q<\/em>and\u00a0q<\/em>.\u00a0Q<\/em>\u00a0is dominant to\u00a0q<\/em>\u00a0and the inheritance of this gene is Mendelian. Answer the following questions about this gene.\r\n
\r\n \t- If a woman has the genotype\u00a0Q q\u00a0<\/em>and her husband has the genotype\u00a0QQ<\/em>, list each of their possible gametes. What proportion of their gametes will have each allele?<\/li>\r\n \t
- What are the likely proportions of their offspring beingQQ<\/em>,Qq<\/em>, or\u00a0qq<\/em>?<\/li>\r\n \t
- Is this an autosomal trait or an X-linked trait? How do you know?<\/li>\r\n \t
- What are the chances of their offspring exhibiting the dominant\u00a0Q\u00a0<\/em>trait? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t
- Explain why fathers always pass their X chromosome down to their daughters.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.13 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=emb_logo\r\nPunnett Squares and Sex-Linked Traits, Amoeba Sisters, 2015.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4\r\n
Pedigrees, Amoeba Sisters, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=veB31XmUQm8\r\n
Secrets of the X chromosome - Robin Ball, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.13.1<\/strong>\r\n\r\nAlbino_baby_by_Felipe_Fernandes<\/a>\u00a0by Felipe Fernandes<\/a> on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0) license.\r\n\r\nFigure 5.13.2<\/strong>\r\n\r\nPedigree_Chart2.svg<\/a> by Jerome Walker on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Derivative work of original image<\/a>\u00a0created by\u00a0GAThrawn22<\/a>)\r\n\r\nFigure 5.13.3<\/strong>\r\n\r\nPunnett square by Christine Miller is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.4<\/strong>\r\n\r\nInheritance of Sex Chromosomes<\/a> by CK-12 Foundation<\/a> is used under a CC BY-NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n \u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 5.13.5<\/strong>\r\n\r\nRed-Green Colour Blindness<\/a> by Unknown author on Wikimedia is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\u00a0(Original believed to be by Shinobu Ishihara<\/a>)\r\n\r\nFigure 5.13.6<\/strong>\r\n\r\nXlinkRecessive<\/a> by US\u00a0National Institutes of Health<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.7<\/strong>\r\n\r\nThe_Young_Queen_Victoria (painted portrait<\/a> by Franz Xaver Winterhalter<\/a> (photograph from the Osborne House, Isle of Wight) on Wikimedia Commoons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.8<\/strong>\r\n\r\nDeuteranopia\/ Figure 9.10<\/a>\u00a0by Web Style Guide<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 5.13.9<\/strong>\r\n\r\n \t- LED traffic light<\/a> by Bidgee<\/a> on Wikimedia <\/i>is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.<\/li>\r\n \t
- Universal indicator paper<\/a> by Bordercolliez<\/a> on Wikimedia <\/em>is used under a CC0 1.0<\/a>\r\nPublic Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en)<\/li>\r\n \t
- Photo tags: Fruit tomatoes food fruits and vegetables fresh<\/a> by InspiredImages<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n \t
- Simple Control with Indicator LIghts<\/a> by Sam D. Wilbur<\/a> on Wikimedia is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/li>\r\n \t
- Photo tags: Feet socks checkered striped pants colorful color<\/a> by Suppenkasper<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\n
References<\/h2>\r\n
Amoeba Sisters. (2015, January 23).\u00a0 Punnett squares and sex-linked traits. YouTube. https:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=youtu.be<\/p>\r\n
Amoeba Sisters. (2017, February 8). Pedigrees. YouTube. https:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4&feature=youtu.be<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 3 Inherited traits of sex chromosomes [digital image]. In CK-12 College Human Biology\u00a0<\/em>(Section 5.12) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/5.12\/<\/p>\r\nmahalodotcom. (2011, January 14). Learn biology: How to draw a punnett square. YouTube. https:\/\/www.youtube.com\/watch?v=prkHKjfUmMs&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 18). Secrets of the X chromosome - Robin Ball. YouTube. https:\/\/www.youtube.com\/watch?v=veB31XmUQm8&feature=youtu.be<\/span><\/p>\r\nWikipedia contributors. (2020, June 26). Albinism in humans. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Albinism_in_humans&oldid=964622728<\/p>\r\nWikipedia contributors. (2020, June 29). Gregor Mendel. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Gregor_Mendel&oldid=965090119<\/p>\r\nWikipedia contributors. (2020, June 17). Ishihara test. In\u00a0Wikipedia. <\/i>https:\/\/en.wikipedia.org\/w\/index.php?title=Ishihara_test&oldid=963014774<\/p>","rendered":"
<\/p>\nFigure 5.13.1 Like mother, like son.<\/em><\/figcaption><\/figure>\n\nAlbinism<\/h1>\n<\/div>\n
This child has much lighter skin and\u00a0hair\u00a0than his parents. He has a condition called albinism<\/a>, which results from a\u00a0lack of\u00a0the\u00a0pigment melanin in the\u00a0skin,\u00a0hair, and\u00a0eyes. Although\u00a0he\u00a0looks<\/em>\u00a0different than his parents, albinism is actually a genetic trait.\u00a0Genetic traits<\/strong>\u00a0are characteristics that are encoded in\u00a0DNA. Most forms of albinism are recessive, which\u00a0is why\u00a0the child’s\u00a0parents were able to\u00a0pass\u00a0the trait to him without exhibiting the condition themselves. You will learn more about this type of inheritance\u00a0in this concept.\u00a0Albinism is\u00a0one of the few human traits that actually has a simple inheritance pattern,\u00a0similar to\u00a0the traits that Gregor\u00a0Mendel<\/a>\u00a0studied in\u00a0pea plants. The way these traits are inherited by offspring from their parents is called Mendelian inheritance<\/a>.<\/p>\n\nWhat Is Mendelian Inheritance?<\/h1>\n<\/div>\n
Mendelian inheritance<\/strong>\u00a0refers to the inheritance of traits controlled by a single gene with two\u00a0alleles<\/a>, one of which may be completely dominant<\/a> to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on autosome<\/a>s, or by genes on sex\u00a0chromosomes<\/a>.<\/p>\n\n- Autosomal traits<\/strong>\u00a0are controlled by genes on one of the 22 pairs of human autosomes<\/a>. Autosomes are all the\u00a0chromosomes\u00a0except the X or Y chromosome, and they do not differ between males and females, so autosomal traits are inherited in the same way, regardless of the sex of the parent or offspring.<\/li>\n
- Traits controlled by genes on the sex\u00a0chromosomes\u00a0are called\u00a0sex-linked traits<\/a>.<\/strong>\u00a0Because of the small size of the Y chromosome, most sex-linked traits are controlled by genes on the X chromosome. These traits are called\u00a0X-linked traits<\/a><\/strong>. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits, because males have just one X chromosome. In addition, males always inherit their X chromosome from their mother, and they pass on their X chromosome to all of their daughters, but none of their sons.<\/li>\n<\/ul>\n\n
Studying Inheritance Patterns<\/h1>\n<\/div>\n
There are two very useful tools for studying how traits are passed from one generation to the next. One tool is a\u00a0pedigree, and the other is a Punnett square.<\/p>\n
Pedigree<\/h2>\n
The chart below (Figure 5.13.2) is called a pedigree<\/a><\/strong>. A pedigree shows how a trait is passed from generation to generation within a family.\u00a0A pedigree can show, for example, whether a Mendelian trait is an autosomal<\/a> or X-linked<\/a> trait. It can also be used to infer the genotype of different members of the family.<\/p>\nThe trait represented by\u00a0this\u00a0chart is a hypothetical autosomal trait controlled by a dominant allele. At the top of the pedigree, you can see symbols representing a married couple. The husband\u00a0has<\/em> the trait (affected male), but the wife does not (unaffected female). The next row of the pedigree shows the couple’s children, as well as the spouses of three of the children. For example, the first child on the left is an affected male married to an unaffected female. The third row of the pedigree shows the next generation (the grandchildren of the couple at the top of the pedigree). One child in this generation \u2014 the affected female on the left \u2014 is the sibling of an unaffected male.<\/p>\nFigure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em><\/figcaption><\/figure>\n
Figure 5.13.8 Perception of colours comparison.<\/em>[\/caption]\r\n\r\nBeing colour blind can cause a number of problems. These may range from minor frustrations to outright dangers. Here are a few examples:\r\n- \r\n \t
- If you are colour blind, it may be difficult to colour-coordinate clothing and furnishings. You may end up wearing colour combinations that people with normal colour vision think are odd or clashing.<\/li>\r\n \t
- Many LED indicator lights are red or green.\u00a0Power strips and electronic devices, for example, may have indicator lights to show whether they are on (green) or off (red).<\/li>\r\n \t
- Test strips for pH, hard water, swimming pool chemicals, and other common tests are also often colour coded. Litmus paper for testing pH, for example, turns red in the presence of an acid, but if you are colour blind, you may not be able to read the test result.<\/li>\r\n \t
- Do you like your steak well done? If you are colour blind, you may not be able to tell if the meat is still undercooked (red) or grilled just right. You also may not be able to distinguish ripe (red) from unripe (green) fruits and vegetables, such as tomatoes. And some foods, such as dark green spinach, may look more like mud than food, making them totally unappetizing.<\/li>\r\n \t
- Weather maps often are colour coded. Is that rain (green) in your forecast, or a wintry mix of sleet and freezing rain (pink or red)? If you can't tell the difference, you may go out on the roads when you shouldn't, putting yourself in danger.<\/li>\r\n \t
- Being able to distinguish red from green traffic lights may be a matter of life or death. This can be very difficult for someone with red-green colour blindness. In some countries, people with this vision defect are not allowed to drive.<\/li>\r\n<\/ul>\r\n[h5p id=\"508\"]\r\n\r\nFigure 5.13.9\u00a0 Examples of challenges faced by those who are colour blind<\/em>\r\n\r\n
\r\n 5.13 Summary<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- [pb_glossary id=\"2515\"]Mendelian inheritance[\/pb_glossary] refers to the inheritance of traits controlled by a single [pb_glossary id=\"5521\"]gene[\/pb_glossary] with two [pb_glossary id=\"5449\"]alleles[\/pb_glossary], one of which may be completely dominant to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on [pb_glossary id=\"2112\"]autosomes[\/pb_glossary], or by genes on [pb_glossary id=\"2125\"]sex chromosomes[\/pb_glossary].<\/li>\r\n \t
- Two tools for studying inheritance are [pb_glossary id=\"2519\"]pedigrees[\/pb_glossary] and\u00a0[pb_glossary id=\"2520\"]Punnett squares[\/pb_glossary]. A pedigree is a chart that shows how a trait is passed from generation to generation within a family. A Punnett square is a chart that shows the expected ratios of possible [pb_glossary id=\"6039\"]genotypes[\/pb_glossary] in the offspring of two parents.<\/li>\r\n \t
- Examples of human autosomal Mendelian traits include albinism and Huntington's disease. Examples of human X-linked traits include red-green colour blindness and hemophilia.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n 5.13 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- Define genetic traits and Mendelian inheritance.<\/li>\r\n \t
- [h5p id=\"509\"]<\/li>\r\n \t
- Explain why autosomal and X-linked Mendelian traits have different patterns of inheritance.<\/li>\r\n \t
- Identify examples of human autosomal and X-linked Mendelian traits.<\/li>\r\n \t
- Imagine a hypothetical human gene that has two alleles,Q<\/em>and\u00a0q<\/em>.\u00a0Q<\/em>\u00a0is dominant to\u00a0q<\/em>\u00a0and the inheritance of this gene is Mendelian. Answer the following questions about this gene.\r\n
- \r\n \t
- If a woman has the genotype\u00a0Q q\u00a0<\/em>and her husband has the genotype\u00a0QQ<\/em>, list each of their possible gametes. What proportion of their gametes will have each allele?<\/li>\r\n \t
- What are the likely proportions of their offspring beingQQ<\/em>,Qq<\/em>, or\u00a0qq<\/em>?<\/li>\r\n \t
- Is this an autosomal trait or an X-linked trait? How do you know?<\/li>\r\n \t
- What are the chances of their offspring exhibiting the dominant\u00a0Q\u00a0<\/em>trait? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t
- Explain why fathers always pass their X chromosome down to their daughters.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n 5.13 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=emb_logo\r\nPunnett Squares and Sex-Linked Traits, Amoeba Sisters, 2015.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4\r\n
Pedigrees, Amoeba Sisters, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=veB31XmUQm8\r\n
Secrets of the X chromosome - Robin Ball, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.13.1<\/strong>\r\n\r\nAlbino_baby_by_Felipe_Fernandes<\/a>\u00a0by Felipe Fernandes<\/a> on Wikimedia Commons is used under a CC BY-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/2.0) license.\r\n\r\nFigure 5.13.2<\/strong>\r\n\r\nPedigree_Chart2.svg<\/a> by Jerome Walker on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license. (Derivative work of original image<\/a>\u00a0created by\u00a0GAThrawn22<\/a>)\r\n\r\nFigure 5.13.3<\/strong>\r\n\r\nPunnett square by Christine Miller is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.4<\/strong>\r\n\r\nInheritance of Sex Chromosomes<\/a> by CK-12 Foundation<\/a> is used under a CC BY-NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n\r\n
\u00a9<\/span>CK-12 Foundation<\/a> Licensed under\u00a0<\/span><\/a>\u00a0\u2022\u00a0<\/span>Terms of Use<\/a>\u00a0\u2022\u00a0<\/span>Attribution<\/a>\r\n\r\nFigure 5.13.5<\/strong>\r\n\r\nRed-Green Colour Blindness<\/a> by Unknown author on Wikimedia is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\u00a0(Original believed to be by Shinobu Ishihara<\/a>)\r\n\r\nFigure 5.13.6<\/strong>\r\n\r\nXlinkRecessive<\/a> by US\u00a0National Institutes of Health<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.7<\/strong>\r\n\r\nThe_Young_Queen_Victoria (painted portrait<\/a> by Franz Xaver Winterhalter<\/a> (photograph from the Osborne House, Isle of Wight) on Wikimedia Commoons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 5.13.8<\/strong>\r\n\r\nDeuteranopia\/ Figure 9.10<\/a>\u00a0by Web Style Guide<\/a> on Flickr<\/a> is used under a CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.\r\n\r\nFigure 5.13.9<\/strong>\r\n- \r\n \t
- LED traffic light<\/a> by Bidgee<\/a> on Wikimedia <\/i>is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.<\/li>\r\n \t
- Universal indicator paper<\/a> by Bordercolliez<\/a> on Wikimedia <\/em>is used under a CC0 1.0<\/a>\r\nPublic Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en)<\/li>\r\n \t
- Photo tags: Fruit tomatoes food fruits and vegetables fresh<\/a> by InspiredImages<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n \t
- Simple Control with Indicator LIghts<\/a> by Sam D. Wilbur<\/a> on Wikimedia is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/li>\r\n \t
- Photo tags: Feet socks checkered striped pants colorful color<\/a> by Suppenkasper<\/a> on Pixabay<\/a> is used under the Pixabay License<\/a>\u00a0(https:\/\/pixabay.com\/service\/license\/).<\/li>\r\n<\/ul>\r\n
References<\/h2>\r\n
Amoeba Sisters. (2015, January 23).\u00a0 Punnett squares and sex-linked traits. YouTube. https:\/\/www.youtube.com\/watch?v=h2xufrHWG3E&feature=youtu.be<\/p>\r\n
Amoeba Sisters. (2017, February 8). Pedigrees. YouTube. https:\/\/www.youtube.com\/watch?v=Gd09V2AkZv4&feature=youtu.be<\/p>\r\n
Brainard, J\/ CK-12 Foundation. (2016). Figure 3 Inherited traits of sex chromosomes [digital image]. In CK-12 College Human Biology\u00a0<\/em>(Section 5.12) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/5.12\/<\/p>\r\n
mahalodotcom. (2011, January 14). Learn biology: How to draw a punnett square. YouTube. https:\/\/www.youtube.com\/watch?v=prkHKjfUmMs&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 18). Secrets of the X chromosome - Robin Ball. YouTube. https:\/\/www.youtube.com\/watch?v=veB31XmUQm8&feature=youtu.be<\/span><\/p>\r\n
Wikipedia contributors. (2020, June 26). Albinism in humans. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Albinism_in_humans&oldid=964622728<\/p>\r\n
Wikipedia contributors. (2020, June 29). Gregor Mendel. In Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Gregor_Mendel&oldid=965090119<\/p>\r\n
Wikipedia contributors. (2020, June 17). Ishihara test. In\u00a0Wikipedia. <\/i>https:\/\/en.wikipedia.org\/w\/index.php?title=Ishihara_test&oldid=963014774<\/p>","rendered":"
<\/p>\n
Figure 5.13.1 Like mother, like son.<\/em><\/figcaption><\/figure>\n \nAlbinism<\/h1>\n<\/div>\n
This child has much lighter skin and\u00a0hair\u00a0than his parents. He has a condition called albinism<\/a>, which results from a\u00a0lack of\u00a0the\u00a0pigment melanin in the\u00a0skin,\u00a0hair, and\u00a0eyes. Although\u00a0he\u00a0looks<\/em>\u00a0different than his parents, albinism is actually a genetic trait.\u00a0Genetic traits<\/strong>\u00a0are characteristics that are encoded in\u00a0DNA. Most forms of albinism are recessive, which\u00a0is why\u00a0the child’s\u00a0parents were able to\u00a0pass\u00a0the trait to him without exhibiting the condition themselves. You will learn more about this type of inheritance\u00a0in this concept.\u00a0Albinism is\u00a0one of the few human traits that actually has a simple inheritance pattern,\u00a0similar to\u00a0the traits that Gregor\u00a0Mendel<\/a>\u00a0studied in\u00a0pea plants. The way these traits are inherited by offspring from their parents is called Mendelian inheritance<\/a>.<\/p>\n
\nWhat Is Mendelian Inheritance?<\/h1>\n<\/div>\n
Mendelian inheritance<\/strong>\u00a0refers to the inheritance of traits controlled by a single gene with two\u00a0alleles<\/a>, one of which may be completely dominant<\/a> to the other. The pattern of inheritance of Mendelian traits depends on whether the traits are controlled by genes on autosome<\/a>s, or by genes on sex\u00a0chromosomes<\/a>.<\/p>\n
- \n
- Autosomal traits<\/strong>\u00a0are controlled by genes on one of the 22 pairs of human autosomes<\/a>. Autosomes are all the\u00a0chromosomes\u00a0except the X or Y chromosome, and they do not differ between males and females, so autosomal traits are inherited in the same way, regardless of the sex of the parent or offspring.<\/li>\n
- Traits controlled by genes on the sex\u00a0chromosomes\u00a0are called\u00a0sex-linked traits<\/a>.<\/strong>\u00a0Because of the small size of the Y chromosome, most sex-linked traits are controlled by genes on the X chromosome. These traits are called\u00a0X-linked traits<\/a><\/strong>. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits, because males have just one X chromosome. In addition, males always inherit their X chromosome from their mother, and they pass on their X chromosome to all of their daughters, but none of their sons.<\/li>\n<\/ul>\n
\nStudying Inheritance Patterns<\/h1>\n<\/div>\n
There are two very useful tools for studying how traits are passed from one generation to the next. One tool is a\u00a0pedigree, and the other is a Punnett square.<\/p>\n
Pedigree<\/h2>\n
The chart below (Figure 5.13.2) is called a pedigree<\/a><\/strong>. A pedigree shows how a trait is passed from generation to generation within a family.\u00a0A pedigree can show, for example, whether a Mendelian trait is an autosomal<\/a> or X-linked<\/a> trait. It can also be used to infer the genotype of different members of the family.<\/p>\n
The trait represented by\u00a0this\u00a0chart is a hypothetical autosomal trait controlled by a dominant allele. At the top of the pedigree, you can see symbols representing a married couple. The husband\u00a0has<\/em> the trait (affected male), but the wife does not (unaffected female). The next row of the pedigree shows the couple’s children, as well as the spouses of three of the children. For example, the first child on the left is an affected male married to an unaffected female. The third row of the pedigree shows the next generation (the grandchildren of the couple at the top of the pedigree). One child in this generation \u2014 the affected female on the left \u2014 is the sibling of an unaffected male.<\/p>\n
Figure 5.13.2 A pedigree chart is similar to a family tree. It shows how a trait is passed from parents to offspring in a family. The trait represented by this pedigree is an autosomal dominant trait.<\/em><\/figcaption><\/figure>\n - Traits controlled by genes on the sex\u00a0chromosomes\u00a0are called\u00a0sex-linked traits<\/a>.<\/strong>\u00a0Because of the small size of the Y chromosome, most sex-linked traits are controlled by genes on the X chromosome. These traits are called\u00a0X-linked traits<\/a><\/strong>. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits, because males have just one X chromosome. In addition, males always inherit their X chromosome from their mother, and they pass on their X chromosome to all of their daughters, but none of their sons.<\/li>\n<\/ul>\n
- Universal indicator paper<\/a> by Bordercolliez<\/a> on Wikimedia <\/em>is used under a CC0 1.0<\/a>\r\nPublic Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en)<\/li>\r\n \t
- What are the likely proportions of their offspring beingQQ<\/em>,Qq<\/em>, or\u00a0qq<\/em>?<\/li>\r\n \t
- If a woman has the genotype\u00a0Q q\u00a0<\/em>and her husband has the genotype\u00a0QQ<\/em>, list each of their possible gametes. What proportion of their gametes will have each allele?<\/li>\r\n \t
![Albino_baby_by_Felipe_Fernandes<\/a>\u00a0by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Albino_baby_by_Felipe_Fernandes_07.jpg\"){kind=link}
![Pedigree_Chart2.svg<\/a> by Jerome Walker on Wikimedia Commons is used under a](\"https:\/\/commons.wikimedia.org\/wiki\/File:Autosomal_Dominant_Pedigree_Chart2.svg\"){kind=link}
![image<\/a>\u00a0created by\u00a0](\"https:\/\/commons.wikimedia.org\/wiki\/File:Autosomal_Dominant_Pedigree_Chart.svg\"){kind=link}
![Red-Green Colour Blindness<\/a> by Unknown author on Wikimedia is released into the](\"https:\/\/commons.wikimedia.org\/wiki\/File:Ishihara_9.png\"){kind=link}
![XlinkRecessive<\/a> by US\u00a0](\"https:\/\/commons.wikimedia.org\/wiki\/File:XlinkRecessive.jpg\"){kind=link}
![The_Young_Queen_Victoria (painted portrait<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:The_Young_Queen_Victoria.jpg\"){kind=link}
![LED traffic light<\/a> by](\"https:\/\/commons.wikimedia.org\/w\/index.php?title=File:LED_traffic_light.jpg&oldid=248599431\"){kind=link}
![Universal indicator paper<\/a> by](\"https:\/\/commons.wikimedia.org\/w\/index.php?title=File:Universal_indicator_paper.jpg&oldid=425236425\"){kind=link}
![Simple Control with Indicator LIghts<\/a> by](\"https:\/\/commons.wikimedia.org\/w\/index.php?title=File:SIMPLE_CONTROL_WITH_INDICATOR_LIGHTS.jpg&oldid=298043241\"){kind=link}